Typically it should say somewhere on the battery if it's gel or not. VRLA and AGM are other names they may go by. They are slightly different techs but basically would fall under Gel.
If there are caps on the battery that are easily removed then it's probably a wet cell. If you need more than light force to pry them open then don't try further, as even sealed types may have caps but those are not meant to be opened.
If it is in fact a wet cell then make sure to actually check it once in a while as you may need to add distilled water if you see the water level is low. If cared for, wet cells will last a very long time.