You can find a list of all your suggested edits in your profile under Activity > all actions > suggestions. Clicking on "rejected edit" will list the reject reasons for that edit. (Most of the time, reviewers will select a reason from the list. See here for the complete list of reject reasons.)
In addition, the next time you try to suggest an edit, you will be told that your previous edit was rejected. (Unfortunately, it's pretty easy to miss the banner. You do not get any inbox notifications either for rejected edits.)
If you're referring to this edit, I was one of the reviewers that rejected it. My reasoning is: the answerer should be in charge of what sources they use because any downvotes on the post will affect their reputation if the source is problematic. If you think including the source will help the answer, you can leave a comment and let the answerer decide if they will include it or not.
(Note that the post owner will be notified of all suggested edits on their post. The post owner can single-handedly decide if the edit should be approved or rejected, even if it means overturning the decision made by reviewers.)