1
Could you tell me what is the problem?
Could you tell me what the problem is?
Please tell me what direction did he go.
Please tell me what direction he went.
In indirect questions, put the subject before the verb: ‘what the problem is’, not ‘what is the problem’. We also remove did and use the past form of the main verb: ‘what direction he went’, not ‘what direction did he go’.
2
I will tell her everything what I know.
I will tell her everything (that) I know.
He will never admit all what he did.
He will never admit all (that) he did.
After everything or all, use that or no word: ‘everything (that) I know’, ‘all (that) he did’.
Use what on its own when it means ‘the things that’: ‘I will tell her what I know.’
See WHICH (2)