Translation:I saw Daniel asking his grandparents about my mother.
The pronoun is implied in this case. If it were about Daniel's mother, then it would be "despre mama SA/LUI. If it were about someone else's mother (not Daniel's or the speaker's) it would be "despre mamă". When Romanians talk about their own parents, they drop the possesive pronoun (sa, lui, ei, lor ecc.) and use the articulated form of the noun. Example: Am fost cu mama la plajă = I went with my mother to the beach. If it were about someone else's mother the sentence would be: Am fost cu mama EI la plajă = I went with HER mother at the beach. In this case you cannot lose the pronoun.
It is not wrong to use the possesive pronoun (mama MEA), but it can be left out in this case.