I would have 2 thoughts:
1) Pool epoxy around the rim of the skimmer INSIDE the pool to seal it--but I don't think I'd do this on vinyl.
2) Lower the water till the skimmer is dry and replace whatever is broken--either the frame or skimmer is cracked or the gasket is torn or crimped.

You don't want to seal it from the outside--that will cause water to back up and rot the walls.