Comments in the moderation queue have the type C_QUEUED (A_QUEUED and Q_QUEUED for answers and questions respectively). To delete them directly from the database you could run
DELETE FROM qa_posts WHERE type = 'C_QUEUED';
Note, however, that deleting data directly from the database backend is usually not recommended and may result in data inconsistencies (see for example this post from pupi1985).
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.