No. Fleas themselves cannot have fleas, but they can have these things called "mites".
No flea collars don't kill fleas they only get ride of them but not kill them
Fleas can be trained by putting them in a jar with a lid. After a while you can remove the lid but the fleas won't jump any higher than they did when the lid was there. So they say.
Probably not. they are used to get rid of fleas.