So i have an answer here, but i need to know how to ask question for that answer:
ans:he is his 3rd son.
que: which son is he to him??
Is that question framing correct? Thanks.
Please see this answer over at English Language & Usage.
The short answer is, “There is no good phrase for that in English.” You can ask something like, “What is his birth order?” or, “What number child is your son?” but these questions don’t sound quite natural. For whatever reason, it’s not something common enough in English to get a simple expression, even though it may be a very common question in other languages.
Instead, we tend to ask something like:
How many sons do you have? And is he your first son, second son …?
How many children do you have? Is he your first-born son?
Or if you’re talking to someone:
How many siblings do you have? Are you the eldest/middle/youngest?
The first question establishes a context where we can then talk about birth order. But it’s unusual to ask about birth order directly, without asking about the total number of children.