they have a lttle different. 你干了什么？notes the verbe 你干什么了？notes the object but we usually do not distiguish them.you can use both of them

In these two sentences, it's same.

没有区别

“今天干了什么？”---What did you do today？ “今天你干什么了？”grammatically is the same to“今天你干了什么了？”---What have you done today？

there is alose the 3rd version 今天你干了什么了