Only using a questioner, there has to be at least one incorrect answer.
Each correct answer gives 30 xp, so you won’t receive any if you use spam kits.
Besides that, Fishtopia, Farmchain (using the water or researching method) and Tag Domination are all good game modes to grind. Besides that, there isn’t any other way.
I personally recommend Farmchain, because basically everything gives you xp.
Water–50 xp
Research 30 xp
Planting I forgot, but it gives 30-50 xp, depending on the crop
Other fun functions— gives 30 xp to a lot more…