Formal:
* Спасибо за вопрос. (Spasibo za vopros.) - This is the most literal and formal way to say it.
* Благодарю вас за вопрос. (Blagodaryu vas za vopros.) - This is a more polite and formal way to express thanks.
Informal:
* Спасибо, что спросил(а). (Spasibo, chto sprosil(a).) - This is a more casual way to say it, literally translating to "Thank you for asking."
* Спасибо за вопрос! (Spasibo za vopros!) - This is a more friendly and informal way to say it.
* Не за что! (Ne za chto!) - This is a common way to respond to "Thank you," and can also be used to say "You're welcome" or "No problem."
You can also choose to use a more specific phrase depending on the context:
* Я рад(а), что ты спросил(а). (Ya rad(a), chto ty sprosil(a).) - "I'm glad you asked."
* Это хороший вопрос. (Eto khoroshy vopros.) - "That's a good question."
The best way to choose the right phrase is to consider your relationship with the person you're talking to and the overall tone of the conversation.