does Exposed uses reflection only for DAO mode, or there is reflection usage in DSL as well?

Yes, it is used for column cloninig at least.

can you point me to some sample usage? I’m also curious if it has an impact on Exposed performance on scale - do you have any data on it?

It should not have any impact as it's called only on an initialization of table definitions (afair).

sounds good, thanks!