No easy answer here I'm afraid.
What sort of handles (I know they'll be wood) but do you want to fix them at just 2 points (top & bottom) as in a C shape or is the handle a D shape, with a full length against the tankard side.
I'd suggest the D shape and it will give a greater glue surface and one that will be long grain to long grain.
You'll need a waterproof glue, so either a Polyurethane glue, like Gorilla or a waterproof aliphatic like Titebond III. But I would suggest that either will still need to be reinforced with a couple of through pegs or a metal strap around the tankard itself.