Receptive Language Answering Questions

Hi my son is almost 3 (in 2 weeks) when I ask him a question like "what are you doing?" he just repeats the question.

However if I tell him, "no answer the question" and ask him again he often (not always) will be able to tell me the answer in simple terms i.e "mummy cars", plane book etc.

I know that it is a processing thing for him because when he answers eventually!! He is always correct. I am waiting for assessment but this will take a few months.

In the mean time how do I help him learn to understand questions and answer them without him repeating it back? I know that we have heaps of other things to work on but he does have lots of words and follows instructions like go get your shoes from your room and bring them to mummy, or put the tissue in the bin etc.