How many conferences will he have spoken at by this time next year?

How many 是疑问词，will 是将来时助动词，have 是完成体助动词，spoken 是 speak 的过去分词。构成 wh-将来完成时疑问句 wh-词 + will + 主语 + have + 过去分词，询问到明年此时这个将来时间点累计完成的动作次数。