Hi alancsears,
Thank you for reaching Microsoft Community.
For the virtual keyboard, do you mean the Touch Keyboard or the On-Screen Keyboard (OSK)?
Touch Keyboard
If it is the Touch Keyboard as shown above, press the &123 key on the lower left corner. You will then see the % key on the top row of the keyboard.
If its the On-Screen Keyboard (OSK) which can be turned on in Windows Settings > Ease of Access > Keyboard, tap Shift key first to enable the Shift function (key should turn blue) then press the 5 key. The % sign should be entered then.