What is the keyboard shortcut to show the connection bar on an existing Remote Desktop session when the connection bar is hidden?
Since that interface requires a mouse to use anyway, I don't believe there is one. You just need to hover your mouse over the top edge to show it.
The knowledge base article "List of the keyboard shortcuts that are available in Windows XP" has a section listing the special shortcuts used while in a Remote Desktop session.
Hovering at the top of the screen will only work is all you did was 'un-pin' the connection bar. However, if prior to connecting you unchecked 'display the connection bar in full screen mode' on RDC's Display tab, then you need a different approach. You cannot bring up the connection bar at all. This may cause you to wonder how to get back to the local computer screen. This is done via the Ctrl + Alt + Pause shortcut key combination which toggles the RDC window size on the local computer's desktop.
The Below Shortcut may work as stated in this windows weblink.
Ctrl+Alt+Home: In full-screen mode, activate the connection bar