Hello, I think I have an idea of why you might be confused by "how do you think" vs "what do you think", you can use "do you think" to make a question less direct. "think" and "suppose" are interchangeable, and the question word (who/what/where/why/when) comes from the original question:
"What will they do to fix the economy?" => "What do you think they will do to fix the economy?"
経済を直すために何をしますか? => 経済を直すために何をするでしょうか?/何をすると思いますか?
"Where did he go last week?" => "Where do you think he went last week?"
先週どこに行きましたか? => 先週どこに行ったでしゅうか?
"How will they fix the economy" => "How do you think they will fix the economy?"
"When will dinner be ready?" => "When do you think dinner will be ready?"
"Why did he leave" => "Why do you think he left?"
You can replace "do you think" with "do you suppose" in any of these ("where do you think they went?", "where do you suppose they went?"). I think it's a dialect thing, I almost always use "think". Someone speaking the American Southern dialect might use "reckon" ("Where do you reckon they went?")