Journal Club - How to encourage students to ask questions to the presenters (peers)
I have taken part in two journal club formats that work well for maximizing student involvement, although whether they would lend themsevles well to assesement, I don't know. 

In both cases the idea is to force everyone to read the paper, and engage with it, and minimise the workload for person "presenting". In neither case is there any powerpoints, or pre-rehearsed talking. The presentor is more of a facilitator. 

Structure one: Figures presented at random

In this structure the person who picked the paper gives a brief introduction to the paper and why they picked it (no more than say 5 minutes). They then present the first figure. 

Subsequent figures/tables are then presented by people selected at random (we roll a die). When I say "presented" I often mean "leads a discussion" - as there might be things in the figure the person chosen doesn't understand, has questions about, particularly since they didn't pcik the paper.

I find that this forces everyone to read and engage with the paper, but it doesn't force the discussion to go beyond what is in the figures.

Structure two: Everyone must ask a question

Again the paper selector introduces the paper briefly. We then go round the room and everyone has to say one thing they liked about the paper, one thing they didn't like, and one question/discussion point. The paper selector writes down the discussion points/questions, prioritises them and the leads a discussion with this as the agenda.