Consider:
I would like to review all thatall that I learnt.
I would like to review whatwhat I learnt.
I am willingthink these two are fine, but I'd like to know the reason why all what iswould be incorrect.
Furthermore, as I can not find my answer yet, so I ca not ab able to present any helpful context.
Therefore, wouldCould anyone possibly readily elaborate it, so that I cancould understand it well?
Thanks in advance!