Most states will allow you to pull a tube or something behind the Jet Ski as long as you have a spotter but some states may not allow you to pull a tube or anything with a Jet Ski with or without a spotter.
And to pull a tube or anything else behind a Jet Ski you need to have mirrors but the laws can vary depending on locality so it's best to get the information on local laws to be sure.
If you're caught you might just get a warning about it but then again you might get a fine as it depends on the officer who spots you.