Hi Son,
In the Media Pool you can set the 'usage' column to be visible in list view and then right click in the Media Pool and choose “Update usage” to refresh the information shown in the Usage column to reflect how many times each clip is used in the project. Info is in the manual.

- Screen Shot 2018-07-20 at 11.56.54 am.png (71.69 KiB) Viewed 1529 times
You can also use 'match frame' when the source clip is loaded into the source viewer and the viewer is the active window. This will reveal the clip in the timeline if it has been used. You need to use a section of the clip that may have been used, as only actual frames in the timeline can be matched.
Resolve 20.0 Mac OSX 15.5 Sequoia, Monitor 3G, FSI SDI grading monitor.
Mac M1 Studio Max 32GB