Here are some questions you can ask yourself to determine if you think you've found enough resources to stop researching:

1. Are you coming across the same information in multiple, credible sources (i.e. two-three or more)?
2. Have you already found relevant information in different types of sources (i.e. books, journal articles, government publications, newspaper articles – whatever is appropriate for your subject area)?
3. If you added a new angle or subtopic now, would it just complicate your argument rather than strengthen it?
4. Are you starting to collect information that isn’t exactly on your topic?
5. Are you running out of time to actually write/prepare your assignment?
6. Do you have enough information to cover the main points of your topic well (or support your thesis, if applicable)?

Source: https://beryliveylibrary.wordpress.com/2017/12/05/enough-research/