Sorin's Ultimate + Undying

[Poof]

According to jester ability would have to finish resolving before any other triggers are placed on the stack so...idk lol

I think it does trigger and is placed on the stack after sorins ability resolves  and then just fizzles?

[BlackJester]

would undying even trigger? i mean by the time it makes it onto the stack there's no corresponding creature.

It does trigger, but since the creature it is pointing at isn't there anymore, it is countered for lack of legal targets.  (fizzles)