Nothing. The sentence is complete as it is. This is why: "How long will you be?" means "How long will it take for you to arrive?" or "How long will it take you to do what you need to do?" A possible answer might be "I won't be long" or "I'll only be 5 minutes". As you can see, this is a self-standing construction - a subject + verb 'to be' + time phrase. In your example, the direct speech form is 'How much longer will my wife be?', meaning 'When will she arrive?', and the indirect speech is 'I wonder how much longer my wife will be.' That's the whole sentence. Nothing missing.

I was waiting for my wife. ok I wondered how much longer my wife would make me wait for her. I wondered how much longer my wife would be ( inside the shop , for example )

I wondered how much longer would my wife make me wait for her.

"making me wait for her"