SpongeBob has to run around until the King gets tired, then ran up to him and whack him with the bubblewand. I think you have to do this at least 3 times --- you'll see the energy meter on the King going down. It's takes a few whacks to get him, then he'll hand you the jar of jelly, which you should take back to Squigward for your spatula reward.

Hide on the smaller platform near by until the energy sources (the first 2) are gone on the third hit. Jump up right in the middle of the last.

when the king gets tired from shockwaves or what ever hit him but watch out he will make
his jellyfish do his dirty work and when you send him away get the shinys in the tub
hope it helps!