... you are a teacher and you review exams with your students? I really wish I had gone to your school... it used to drive me crazy when we'd get exams back and I'd missed a question and couldn't figure out why it was wrong!
Trading knuffels is a lot like doing any other trade: you start your trade with your person, your inventory pops up. On the left, there's an option that says "knuffel" near where the place you add
or
is.
You click that.
It changes out your wardrobe for your knuffel (even the hidden ones).
You can search by name (thankfully!!!) and then sometimes the first time you click on a knuffel to add after searching, it just rearranges the search results, that's a common bug, just click on the right knuffel again and it will go into the trade.
As far as I know, there's no limit to how many knuffel you can load into a single trade.
I'm storing some 187 knuffel in a trade right now while I try and sort through my army (most of them are the Darkness Trial knuffel, because I love that one, and the current Water generation knuffel, because Anglerfish are awesome and even if they don't normally school, I'm totally building an Anglerfish Army).