[DarkStar]

Like many things in Reaper there is an Action - and you can asign your own shortcut to it:

-- click [Options] , select show Action list,
-- type "fx chain" (without the quotes) into the Filter field,
-- select the Action: Track: View FX chain for current track",
-- in the "Shortcuts for selection action area, click [Add],
-- press the keyboard keys (+ modifier) that you want to assign,
-- click [OK]

You may need to try a few different ones to find one that is not currently used. You can click [Find shortcut] and type your desired shortcut to see if it is already assigned.

HTH