The jury is almost certainly going to think Cohen is a liar - - because he is. He’s contradicted himself and denied saying things that he just said right in front of them, only minutes before.

Even when jurors don't have these kinds of blatant contradictions to consider, they tend to actually be pretty accurate judges of a witness' credibility. That's a good thing, because the jury is specifically tasked with making those kinds of determinations, and then assigning the proper weight to each witnesses' testimony in their deliberations.

Jurors take their roles very seriously. In my experience, they tend to view themselves (whether they know it or not) as balancers - either consciously or subconsciously challenging whichever perspective they're hearing about at the moment. For that reason, I think it is possible that the jurors might actually conclude that Cohen's lack of credibility or questionable moral compass is indicative of the kind or quality of person with whom Trump surrounds (or surrounded) himself - which would ultimately weigh out in favor of the prosecution. In other words - the jurors might decide that Trump's choice to work so closely with someone who is so clearly not trustworthy is a knock against Trump's own character. Sort of a "birds of a feather" heuristic.