I often hear just “哪里去？”

For this sentence, it would be better to add "要“ to emphasize the destination that you are planing to go to. Actually, like English, you can use different expressions to express what you want to say, most of the time they don't have many differences. 你要到哪去？ 你要去哪？ 你去哪？ 去哪呢？ 到哪去？

1.If somebody will go somewhere(on the road) , but he's not there now. You can use “要“.=>你要到那裡？ 2.Or somebody will move on somewhere but he just doesn't move off now. When you see him, you can also use " 要“. Actually , you can also say哪裡去？in 1 and 2 this two conditions.

你要到哪里去？ and 你到哪里去？ are both ok. 要 emphasizes the meaning of present progressive if you are already where you went...we can ask, 你到哪里去了？ 了 can function as the word for present perfect .

你 去 哪儿？