After uploading a Gedcom to WikiTree you should receive an email titled "GEDCOM import complete". Near the top of this email is a link. Clicking this link will bring you to a page that lists all the people in the Gedcom and it also shows which ones were skipped. You may have to scroll down to the bottom of the page to see the information. This is the only way I know how to see a list of the 'skipped' people.
The link in that email stays active forever. If you lose it, it can be found in your contribution list. Search for "GEDMatching" on the date of the upload.
I bury this link in the profiles I manage in case I have one of those "Why did I do that?" moments. Recovering from skipped profiles can be difficult.