Ubuntu using SQL would definitely be on-topic here at Super User. This doesn't mean it would be off-topic in the other sites you mentioned, though - both have tags for windows-subsystem-for-linux. The borders between the different SE sites aren't always clear-cut, and some questions may be appropriate for several sites.

Ubuntu using WSL would definitely be on-topic here at Super User. This doesn't mean it would be off-topic in the other sites you mentioned, though - both have tags for windows-subsystem-for-linux. The borders between the different SE sites aren't always clear-cut, and some questions may be appropriate for several sites.