We can't know if an answer was deleted for a specific reason unless it is deleted as Rude/Abusive or Spam. We can only know if a moderator ad specified a reason in the comment section why he is deleting. We can know easily if it is a pure question, edit or comment (According to SE standards.. not our sites) posted in answers but if they do it for lacking sources, they generally leave a comment.
Users with access to Moderator tools i.e., with >2k reputation can look at some interesting stats, closed posts deleted posts within a range of 30 days. These are popularly known as 10k tools as they are gained at 10k on normal sites.
Deletion of unsourced answers is not happening all the time. Moderators are giving enough time for older answers to update with sources. If there is no response from the other side, they are deleting them. It is happening rarely. But the same is not happening with new users and new posts. Users should consider that giving time for new users too. They are flagging the answers for citation banners or Very Low Quality straight away without educating new users how site works or how answers are to be written. This way should change and we have to give some time for them too.