In:
よし じゃあ 出席取ってくぞ
what does adding "く" mean for the verb?
「てく」is often a contracted form of 「ていく」, so your sentence means
よし、じゃあ出席を取っていくぞ
Okay, I am going to take attendance now.
where 「ていく」is a helping verb that tells you the action starts now in a forward looking manner.