多久 + Verb + 一次
多久 (duōjiǔ) combined with a frequency word like 一次 is used to ask how often something occurs. The construction inquires about the interval between repeated actions, such as "How often do you exercise?"
你多久去一次健身房?
Nǐ duōjiǔ qù yí cì jiànshēnfáng?
How often do you go to the gym?
他多久给家里打一次电话?
Tā duōjiǔ gěi jiālǐ dǎ yí cì diànhuà?
How often does he call home?
你们多久见一次面?
Nǐmen duōjiǔ jiàn yí cì miàn?
How often do you see each other?