How do I see which tax returns have been efiled?

Probably the easiest method is to open the Efile menu, select Reports, then select Current.
You are now shown your efile log.  Note the window on the bottom of the dialogue box shows a summary of the file selected.  If you select the top file, you'll see the name appear in the display box at the bottom of the box.  Use your down arrow key to move down the files while watching the name change in the bottom view box until you find the file you are looking for.  You an also double click the file to open it and see a larger screen of the same message.

A fast way to look up the exact date and time the file was transmitted is to open the file, click the Save button, and review the save log that appears in the dialogue box.  This log shows the date and time the file was e-filed and whether the file was Accepted.  You can then use the E-file Report log to find the file matching that time specific time.

Hope this helps.