Make sure your skill in one-handed or two-handed is 61 or higher, otherwise the sword won't pop up. If your skills are in the clear there might be something else at fault, like script lag.

i spawned it in, due to impatientness, thanks though!

Can't seem to spawn it or get it by killing it,

I assume you're not able to console it in on top of not getting it after killing the Reaper? If that's the case make sure the mod's active by checking the Data Files section in the default launcher. If it is try changing its position in the load order.

how do i spawn it? i've tried most of the commands that i know but nothing happens

Use player.additem to add it directly to your inventory. You'll need to type "help tenebrae" (sans quotes) to find out the item ID. If that doesn't work then chances are the mod isn't active.