There are a few Skype command line switches documented on the Skype support site:
https://support.skype.com/en/faq/FA171/can-i-run-skype-for-windows-desktop-from-the-command-line

However, it seems that the list isn’t complete. From a post on the Skype community site (the post doesn’t seem to be available any more) I found the following additions:

This will start Skype with the specified account name and password:
"C:\Program Files\Skype\Phone\Skype.exe" /username:your user name /password:your password

This will start a “portable” Skype installed at “path to skype.exe” with all data being saved in the “Data” folder:
"path to skype.exe\Skype.exe" /datapath:”Data” /removable