Formal:
* Mayroon akong tanong. (May-roon ak-ong tan-ong.) - This is the most formal way to say it.
* May katanungan po ako. (May ka-tan-un-gan po a-ko.) - This is also formal and uses the polite "po" particle.
Informal:
* May tanong ako. (May tan-ong a-ko.) - This is a more casual way to say it.
* Tanong lang. (Tan-ong lang.) - This means "just a question" and is very informal.
Other variations:
* Gusto ko lang magtanong. (Goo-sto ko lang mag-tan-ong.) - This means "I just want to ask" and is more casual.
* Pwede ba akong magtanong? (Pwe-de ba a-kong mag-tan-ong?) - This means "Can I ask a question?" and is a polite way to ask.
The best way to say it depends on the situation and who you are talking to.