How can I identify DB error?
Detailed instructions are available in the "More detailed errors" section of the troubleshooting guide.  In short: Either turn on debugging AND backtrace, which will give you a more detailed error; or view the appropriate errors in your CiviCRM log.

If you need help interpreting those errors, I suggest opening a new question here.  It's also a good practice to paste the text of the error instead of (or in addition to) a screenshot of the error - it makes it easier for others to search, and easier for someone to troubleshoot.