The control panel site selection menu only appears when the user is assigned a Regular Role that contains an "Access in Control Panel" permission. If the user does not have such a permission, the site selection menu will be replaced with a heading that says [User]'s Personal Site (clicking it will expand/minimize the menu, not provide a selection of sites).

A workaround for this issue used to exist where the user could click the Sites link in control panel and select the desired site, which would navigate the user to that site and simultaneously make the site selection menu visible, but this capability was removed during a recent bug fix (the user now gets an error message after clicking on the site if he/she does not have the View permission for Site Settings).

1.) Add a User
2.) Add a Site
3.) Add a Site Role
4.) Add a Regular Role
5.) Assign the test user to the site
6.) Assign the regular role to the test user
7.) Assign the site role to the test user under the test site
8.) Sign in as the test user
9.) Navigate to control panel
10.) Assert the control panel site selection menu (it will be set to the test user's personal site with no way to change it)
11.) Sign in as the SA user
12.) Define permissions for the site role
13.) Grant the Control Panel: Site >> Web Content >> Access in Control Panel and View permissions to the site role
14.) Repeat steps 8 - 11
15.) Define permissions for the regular role
16.) Grant the Control Panel: Site >> Web Content >> Access in Control Panel and View permissions to the regular role
17.) Sign in as the test user
18.) Navigate to control panel
19.) Assert the control panel site menu (the site selection menu will be available)