It's the informal imperative form of the verb "preguntar" (to ask), conjugated in the second person singular or plural.
Here's a breakdown:
* Preguntar: To ask
* Le: To him/her/them (indirect object pronoun)
* Preguntale: Ask him/her/them
Example:
* "Preguntale a Juan si quiere venir." (Ask Juan if he wants to come).
Note: You can use "preguntale" for both singular and plural "him/her/them."