I dont know when im have to add"ing" to have,and in this case what it add to the meanning?
'I fully understand the 'One China' policy, but I don't know why we have to be bound by a 'One China' policy unless we make a deal with China( having) to do with other things, including trade,' said Trump.

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Answer

If you didn’t write “having to do with” you would have to write for instance “that has to do with”.
It would be wrong to write “unless we make a deal with China have to do with...”

Answer

"having to do with XX" means "concerning XX",  "about XX", or "related to XX".
So "we make a deal with China having to do with other things" is like "we make a deal with China about other things'.

Grammatically, you can think of it this way.

1. "have to do with XX" means "(something) concerns XX" or "is related to XX".
ex) The problem of the house has to do with its foundation. (the problem is related to its foundation)

2. a verb can be converted to an adjective by adding -ing to it (-ing form is called a present participle)
ex) A car moves fast => There is a car [moving fast]. - "moving fast" describes "a car".

3. If we apply this '-ing' form to "have to do with ...", we get "having to do with ...".

A: We make a DEAL with China.
B: The DEAL has to do with other things.
C: (Combine A and B) We make a deal with China having to do with other things.