How do you tile on top of tiles?

Sure can, but if its waxed tile you should rough it up unless there's a chance its got asbestos in it. Then use a primer sealer over that top to give the glue something to bind to. Also remember that...

yes you can, but that doesn't mean that it's the best solution. the best way is to remove the old tile. period.

Not really. What would you do at the edges, doors, where it meets carpet ect.

yes, but not advisable.

If its new VCT probably, but it must be down tight & smooth and you will need to strip the old wax & rinse good so there is no stripper residue. It eats adhesive over time.