This is a guide to how to get every achievement in Kathy Rain 2. I've noted instances below in italics where I'm not absolutely certain what exactly caused a particular achievement to pop for me so do please comment if you have any more information.

This guide is absolutely full of spoilers.

The following achievements can easily be missed in an ordinary play-through. I've sorted them by in-game days and in approximately the order that they'll be encountered. Make sure to save frequently so that you can return to a certain section if you miss these.

These achievements are not tied to a specific day or have to be completed over multiple days.
Picture purr-fect
In Kathy's office try to take a photo of Mildred the cat with your camera.
Eileen's favorite book
In the library use the computer to search for the Bible.
Enjoying the scenery redux
Simply linger on the biking interstitial screen between levels until this pops.
Serial stroker
This is obtained after stroking Mildred the cat several times (3). You can do this in one day or across a number of days.
Disco lights
Press the button for the pedestrian crossing (Downtown) multiple times.
Zen-tastic
After you've completed Meadow's original task and taken the photo for her, use the crystal in front of Meadow's RV. I think this has to be done on a day when Meadow is present so one might be cut off from doing it on certain later instances when one returns to Meadow's RV. It's worth trying it as soon as you can on day two.
Grand Theft Moto
When in a location where you can still interact with your bike (i.e. it's not parked off-screen) try to use your lock picks on your bike as if you mean to steal it.
The view is always greener...
When visiting various locations always look through the windows and see the views that they present. After you've looked through them all (in one singular run/save) Kathy will comment that everyone has a better view of the city than she does. I think the relevant locations are The Gazette, Longhorn PI, Debra's Cabin and Onyx Row (maybe more) so the earliest that this achievement can be obtained is the evening of day four when you first visit Onyx Row.
Mirror matcher
When you have both the obsidian shard and the obsidian scrying mirror (obtained on day 3) in your inventory, try to combine the two.
Molotov cocktail
Use your lighter on the bottle of whiskey in the PI's office.
Cut lover
One you've obtained the scissors, try to cut Mildred the cat's hair.
Scissor sisters
Once you have the scissors, try to use them on the bonsai tree in Tabby's store.
Old habits
Use your lighter with the cigars in the PI's office or on the cigarettes that you obtain for the cigarette puzzle.
Library buddies
Speak to the librarian each day that you can. This should pop after you speak to him in evening 3 at the Club of Hearts and then speak to him at the library on morning 4. I think you also need to talk to him *about* the club before meeting him there.

Not gonna be that easy
Open up the phone book in Kathy's office and try to look up The Soothsayer. Needless to say, he's not listed, although that'd be nice.
Blasphemous
When talking to Art about his famous case (framed on the wall behind him) choose the three responses that are particularly crude and dismissive about religion. Eileen will huff and this achievement will pop.

A+
Obtained by completing the Debra quiz puzzle in the intended way: by researching and getting all of the answers correct.
F-
Hand in the Debra fandom quiz but with wrong answers. Handing it in without filling it out doesn't count for this. You can do this before handing it in correctly or burning it.
Burning fandom
When you're given the Debra fandom quiz, use your lighter to set it alight. Amazingly, this is actually a legitimate way to solve this puzzle. This is however mutually-exclusive with handing in the completed, correct quiz so you'll need to replay this section to get all of the achievements related to it.
Grand Theft Auto
Try to use your lock picks on the car from the 'Tinkerer' car-fixing puzzle.
Chakra show-off
Use the crystal to meditate in front of Debra's cabin.
Post-zap clarity
For this you need to have gotten the funky chakra crystal off of Meadow before heading to the lookout and encountering the junkie there. After you've zapped the junkie and he's down for the count, use the crystal to have a little chill nearby. If you've had the junkie encounter before you meet with Meadow you'll have to redo this section. There may be extra conditions for this. Update me if you know more.
Double zap redux
Once you've zapped junkie Corey, try to zap him again.
Cabin fever redux
Get caught by the ranger during the snooping-around-the-cabin puzzle.

Button masher
When you first go to Engstrom's, push the door button repeatedly until Oscar reminds you that you need to ask him to buzz you in.
Tea sommelier
During the making-your-own-Royals cigarette puzzle but before you complete it, head to the Gazette and try to add some of your ingredients (lavender, etc) to Art's tea.
Humanist poet/Maverick poet/Survivor poet
These all come about during the haiku puzzle and are all produced by trying out different poems before landing on the correct one. I couldn't remember what I used to get each of these results but according to @LeyZ it's:
"Maverick Poet (All Bottom Options): ♥♥♥♥♥♥ Up Vibes Burn Bright, With Zero Rules, Nothing's Right, Dissent, Feel so right,
Survivor Poet (All Left Options): Booze-filled nights stand proud, Struggling through pain, tears stream down; Madness, Mystified.
Humanist Poet (All Top Options): Skin on skin break free; Through gentle touch, hearts unite; bonding, justified."

Pattern recognition
Once you've encountered Corey sober and seen his graffiti go back to the fire pit and look at the graffiti there.
Quid pro quo
Before going to the Onyx Row apartment in the evening, go Downtown and speak to Lionel. One of the dialogue options will cause Kathy to have a brief aside about how she's not going to share the information she promised him.

Dumpster fire
When you go to revisit the crash site, try to use your lighter on the dumpster.
Anti-pharma
Try to throw away your medication. You can use drain/dumpster at the crash site or the trash can in the PI's office.
Woof woof
When solving the pager puzzle, "1011" can either mean a pair of initials (correct) or "dog case". Guess the latter!
Anti-PC crowd
Once you have the magnet from the dorm room desk try to use it on the computer.
Fridge magnet
Once you have the magnet from the dorm room desk, return to Kathy's bedroom and try to use the magnet with your refrigerator.
Treasure hunter
Once you've combined the magnet and the wire to create an ersatz fishing rod, travel to the fire pit area and try to use this device on the drain beneath the observation platform.
Pacifist
Once you've fished the gun out of the drain at the crash site, return to the PI's office and try to place the gun back in its box.
Bullseye
Once you've obtained the gun, go to Kathy's bedroom and attempt to shoot at her dartboard.

Frankenstein
After you've found the slain Tabitha, try to use your taser to zap her body.
Tom out
During the shootout puzzle in the mines, instruct Tom to go for the valve but then fail to distract Cooper and get Tom shot. If you succeed the puzzle on the first try you'll have to redo this puzzle in order to fail it.
Taunt queen
During the shootout with Cooper, try interacting with Cooper and Kathy will taunt him, eventually needling him about the fact that she successfully hid from him in the cabin days earlier, and this achievement will pop.
Caliber confusion
After the shootout with Cooper is completed and he has fled and dropped his gun, try to combine the ammo from your inventory with his gun.

The following achievements are tied to essential puzzles or game-play milestones and as a result cannot be missed in an ordinary play-through.

Micro sleuth
Obtained by completing the microfilm puzzle.
One more case
Finish the first day.
Tinkerer
Complete the car mechanic puzzle.
Chakra inititate
Complete the first Meadow puzzle.
Chasing leads
Finish the second day.
Rough Royals
Complete the Royals cigarettes puzzle.
They call me the laminator
Complete the membership card puzzle.
Popular poet
Complete the haiku puzzle.
Poetry queen
Finish the third day.
Higher stakes
Finish the fourth day.
Page-restricted
Complete the pager code button.
1337
Complete the computer password puzzle.
Revelations
Finish the fifth day.
Victim number six
Encounter Tabitha's body.
Flew the coop
Complete the shootout puzzle in the mines.
The real daughter
Complete the section in the mines where you encounter your mother and your doppelganger.
Sanctum showdown
Finish the sixth day
Master of Belief/Master of Lament/Master of Reason
Complete the puzzles in the underworld section.
Gun of Revenge
Obtain the weapon in the underworld.
A fate serene
Finish the game.