"manifest" is a very cool word, I don't blame you a bit. But technically, it probably doesn't apply here in any of the OED noun senses:
A document listing a ship’s contents, cargo, passengers, and crew, for
the use of customs officers.
1.1A list of passengers or cargo in an aircraft.
1.2A list of the wagons forming a freight train.
(I doubt that western civilisation will fall if you succumb to temptation and extend definition 1.1 to cover this, though.)
Register is perhaps closer to the mark:
1An official list or record of names or items:
"Sessions manifest / register" probably isn't that appropriate, because the sessions will occur regardless of whether any member of your team attends or not.
Attendance register might be an option; though you could argue that it's not really registering all of the people who attend.
Session assignments register (abbreviated to "the sessions register", abbreviated further to "the register", which is as close to one word as you're likely to get) could do it.
But on the other hand a word that you already used (list) would be just as effective and shorter as well.