I would say, as a first level wizard, unless he's encountered gnolls somewhere in what I assume is the wizard's rich backstory, this is probably his first time encountering gnolls, but I'm sure the wizard reads books, being all wizardy and shit, and he probably has read books that describe gnolls and stuff, so normally yeah, an Intelligence check would probably give you some information on what gnolls might speak, but I'll save you the Ability Check and just tell you I plan for you to find out naturally what language gnolls speak.
I was just waiting to see if Gilly wanted to use her cloak, but I actually think unless she took it off after the ghoul fight (which I don't recall @KCC saying in any posts, she's probably wearing the cloak at the moment anyway. So unless that's not the case, which @KCC can tell me and we can retcon it, lets assume Gilly's still wearing her Elven Cloak.
Also, yeah if you did that to Gilly I'd just give you her cloak as a reward for doing that to her. But also, the module specifically states that that cloak was sized for smaller folk (i.e. halflings and dwarves), so unless you're trying to pass yourself off as a man with no legs, or as a man with only legs, you're not likely to get a ton of use out of it, I imagine.
Also, a quick heads' up... On February 10th I'll be headed to Billings Montana with my daughter and the rest of the family for the Montana High School Wrestling State Championships. It was originally scheduled to be a one day tournament, but there's forty-something girls in my daughter's 113lb bracket alone, so the tournament is now scheduled to run for three days. The day of the 10th they start wrestling at 6pm and will just run late into the night until there's only sixteen girls left.
Maybe my daughter gets beat out before Day 2 of the tournament, but we're expecting her to be seeded #2 for the tournament, so she'll probably have a pretty cushy ride to the final 16. If so, then they'll run the 2nd day (the 11th) through to probably the quarterfinals, and pick it back up on the final day (the 12th) from quarterfinals to the end.
I'm tentatively expecting her to be in the finals for the tournament, so unless something goes south somewhere in the brackets, which is always possible, from the 10th to the 12th I expect my posting may be sporadic and the 10th I definitely expect to run really late into the night, so I might not even get a post in that day.