This tutorial covers finding who has access to a project, and who has access to an entire account.
See everyone on one project
Click the gear icon at the bottom of the left sidebar.
Under Projects, click All projects. The list shows each project's address, how many users it has, and its tier. Use the search box or the Tier filter to narrow it down.
Click the project. It opens on the Users tab.
The table lists each person's name, email, when they were last active, their project role, and their account role. Filter by last active, status, project role, or account role to answer questions like "who on this job has never logged in".
See everyone on the account
Open Settings and click Users under Account. That table covers every user in the account and adds a Projects column showing how many projects each person can reach.
If you do not see the Users tab
It only appears for people with permission to view that project's users. If you land on Details instead, you do not have that permission on that project. Ask an Account Admin on your team.