Has anyone used this product when making jam or jelly. If so, how much should be used per batch? Thank you.

I use it when making beer. You use 1 drop per gallon of liquid

When doing a full boil on a 5 gal batch, do I need to add this right before the boil, or can i add it anytime before that?

You can do it right before boil, or even during boil if you need to "save" it from boiling over. You can also put it in the carboy to tame down foam production.

just wondering if a drop of this could be used to get rid of foam when pouring a picture out of a kegerator-- eliminating foam when pouring out?

Foam Control does not affect the head on your finished beer. In fact, it can actually increase the head by retaining head-forming compounds that would have been blown off during fermentation

Can I use this to stop foam on a carboy from going and foaming pieces to clog the air lock? I'm making some fruit wine if that matters.

Yes you can. I believe it's double the dosage, and ad once it's in the carboy. But honestly, it's a lot easier and cheaper in the long run to get a blowoff hose.