It was bugged?
What does your journal say? And did you ask Grenn for more info about it?

From what I know and what I've read, this mission was always bugged in vanilla but was apparently fixed in TSLRCM.

I did talk to Grenn, and got the quest. But from then, there is not a single NPC that I can progress in the quest with. Right now the journal says:

False Batu: Bonus Mission
An assassin disguised as Batu Rem, a TSF offices on Citadel Station, made an attempt on your life while you were imprisoned there. It might be worth trying to find out who hired him and why.

I tried speaking with Grenn again, but there are no further conversation points offered on that. I tried speaking with the TSF droid, Chodo Habat, Jana Lorso, vendors, etc, but no one has any dialogue options for it. Then I read some more guides and suggestions vary, but the most frequent one is to talk to the two guards at the Czerka dock, apparently you can bribe or persuade them to talk, but again, I'm not getting any dialogue prompts for Batu with them.

Hassat, if I remember correctly I couldn't complete this mission either. What is the progression supposed to look like?

Well i talked to commander then talked to the blue xeno and bribed him for info then talked to twilek and exhausted his dialogue then returned to glen with knowledge that assasin came from cherka and bam mission done.
Reward is garbage tho