Unfortunately there is not a report that provides a list of all of the users and the spaces they have access to. However if you are looking for a specific user, you are able to look up to see if they has access to a space and if they do, what their permission level. This can be done in the Admin Console > Permissions > Space Permissions - this will allow you to chose the space and search for the user. In my example I searched for my user in the New Test Master space:
Hope this helps.