On this (disastrous) "release" CLoD don't come with keyboard sheet or similar, and latter in official and TF patches some commands are changed, others added...
Besides this, different planes can have different/exclusive commands, so are not a "universal" keyboard layout.
E.g. prop pitch command need inverted keys between Spit and Bf 109... Some for magnet switches, some planes use toggle,others use rotary selector.
Better is choose one aircraft, configure then, save the profile - the game controls allow save individual per plane profiles.
In ATAG Flight School are what is need for every plane.
Relative your specific questions.
... how to "switch on" a fighter's gunsight (been practice flying in a Hurricane, but stuck with a blank reflector gunsight)
Toggle gunsight illumination in Hurricane can be done be clicking with mouse in the switch on right side of RPM instrument or using the key/joy button assigned in:Options > Controls > General > Keys
(tab) for:Toggle Gunsight Illumination
Or the keys/buttons for:Increase Gunsight Illumination
Decrease Gunsight Illuminatio
In Bf 109 the gunsight illumination intensity can be adjusted with this command. Spit/Hurri is only ON/OFF.
... and how (if..?) to activate the "speedbar" that we used to get in the lower LH corner with the original Il2 series.
CloD don't have this kind of "HUD" like in IL-2'46, is need read the instruments on panel.