Is white spot on gum line an abscess?

Depends: If it is swollen and especially if it drains like a pimple, it can be an abscess. There are other possibilities like blanching from a external stimulant, like bleaching, or others. See a qualified dentist to evaluate.

Depends: A white spot could be a gumboil, or parulis, which is the drainage area for an abscess. But there are several other reasons for white spots that are unrelated to an abscess. If you have a painful adjacent tooth, or foul tasting drainage from the area then the chance of an abscess is higher. An evaluation by your dentist is the only way to find out the etiology.