Single word request that means 'make a question stronger"
I would use substantiate.
Substantiate
to show something to be true, or to support a claim with facts:
- We have evidence to substantiate the allegations against him.
- Reports that children had been hurt have not been substantiated.
[Cambridge English Dictionary]
Or reinforce
Reinforce
If something reinforces an idea or opinion, it provides more proof or support for it and makes it seem true:
- The final technical report into the accident reinforces the findings of initial investigations.
[Cambridge English Dictionary]