Go to the "Members" page from the left side panel and click on a member's name (who's joining date you'd like to see). You will be taken to the Member details page.
From here, you can see the Joining date of this member.

Go to the "Members" page from the left side panel and click on a member's name (who's joining date you'd like to see). You will be taken to the Member details page.
From here, you can see the Joining date of this member.