你想去对我说 means you want to go to speak to me.
How to ask a question: What do you want to come to talk to me about? I don't know where to put the word 什么
.
Is 你想去对我说什么
correct?
How to say a normal sentence (not a question): This is what I want to go to speak to you.
Is 這就是 我想去对你说什么
correct?
How to ask a question: Is this what you want to come to speak to me?
come
instead ofgo
.go
instead ofcome
,What do you want to come to speak to me?
is still a very peculiar, un-idiomatical sentence. It still means, as @Becky李蓓 mentioned, "what payment or reward do you want for coming to speak to me?".