I am not a native either but I've had this conversation with my professors a few times.  At that time, my doubts were about the necessity to add the indirect pronoun (IOP) 'le' or 'les' when we ACTUALLY specify the indirect object complement (IOC).

Of course when a verb does not have a IOC, you don't need to use the IOP as in:

  * Preguntar <ALGO>.

However when there is an IOC, it is **ALMOST** always necessary in Spanish to put the pronoun (le o les) even though we specify the IOC.  The majority of the verbs in Spanish 'require' it.  For example:

 ** [YES]  Les pregunto algo a mis padres 

 ** [NO]   Pregunto algo a mis padres

  ** [YES]  Le doy un regalo a mi amigo

  ** [NO]   Doy un regalo a mi amigo

I would say that "preguntar" needs a pronoun if you 'know' who is asked. (EDIT: or it sounds more natural).

¿Te preguntaron (a ti) la edad?

Puedes preguntarme (a mí) lo que quieras

Pregúntaselo (a él/ella) mañana.

Le preguntaré a alguien la hora. -> You "know" it grammatically

Vamos a preguntarleS a las personas cual es su profesión ->  You "know" it grammatically

But if you don't know it, "preguntar" doesn't need a pronoun.

Necesito preguntar el precio.

Mañana preguntaré los ejercicios.

(You can write a pronoun, but it's not needed)

I think that is the reason. Removing a pronoun when I "know" who is asked sounds unnatural to me

I hope not to be wrong.

I would like to ask the Commissioner when we can expect this communication.

Señor Presidente, ¿puedo preguntarle si se ha producido algún malentendido?

Mr President, may I enquire if there has been some misunderstanding?

¿Puedo preguntarle al Comisario cómo va a continuar?

Can I ask the Commissioner how he will proceed?

Preguntar es la palabra sin ninguna conjugacion, ni pasado , ni peesente, etc.

Hay que preguntar si mañana hay clases

Mejor hay que preguntar para no equivocarnos

Espero te ayude