But the “mein” is there and I wouldn’t call it a pronoun in this case. If it’s used before a noun like in “mein Geld” then it’s just a possessive determiner.
Determiners are a more general class of words that include for example articles. Mein is not acting as a pronoun in the example sentence but more like an article.
Grammatically correct would be “Wo ist mein Geld?” The “mein” is The missing pronoun.
But the “mein” is there and I wouldn’t call it a pronoun in this case. If it’s used before a noun like in “mein Geld” then it’s just a possessive determiner.
Since I have no clue what the latter is I sadly can not say if this is the case or not.
Determiners are a more general class of words that include for example articles. Mein is not acting as a pronoun in the example sentence but more like an article.