In the following command, what part of speech is 'me'?

díganmelos.

reflexive pronoun
indirect object pronoun
direct object pronoun

The answer is: Indirect object pronoun.

Explanation:

Let's discard the other options first; reflexive pronouns are: Myself, himself, yourself, etc... which is the equivalent in Spanish of: A mí mismo, a sí mismo, a ti mismo, etc... A direct object pronoun is the object that the action is happening, for instance in the following sentece: My mom ate a donut; donut here is the direct object. And well, Indirect object pronouns are: me, him, her, them, us, you... which is basically what "díganmelos" is --in English, tell me--.