疑问词可用 how 加表示经常的副词 often。

如果句子含义 be，应该用 “How often＋ be＋主语＋ ...”，如 How often is he out at night (他晚上多久出去一次)?

如果句子的谓语动词是行为动词，应该用 “How often does/did＋主语＋...”，如 How often does he leave on business (他多长时间出差一次)?