Tafsir of Az-Zumar 39:48

And there appeared to them—at the time when their scrolls are presented to them—the evil deeds of what they earned, meaning that which they earned and did, assuming ma (what) is a relative pronoun. Or [the evil deeds of] their earning and their doing, assuming ma is a verbal noun, with the genitive construction of "evil deeds" being one of min (partitive) or li (possessive).

And there encompassed them—meaning surrounded them—that which they used to mock. That is, the recompense for that, assuming the speech implies an omitted possessor, or that there is a figurative expression here by mentioning the cause and intending its effect. Ma is also potentially a relative pronoun or a verbal noun.