If I load a Mono-Reverb and I want it to be panned, what is the difference between Panning it
via FX’s panner slider Vs The send panner on the dry track itself?
Please let me understand.
If you move the FX channels pan slider, the reverb will go l/r, obvious.
If you move the send panner of the dry track, the reverb will stay centered. Not sure if the the send panners also follow the pan law (never tried tbh) - if they do the send gain might change accordingly (drop in center unless you use constant power).
If you want the mono reverb to follow the send panners position better use either a dual input stereo reverb or two mono reverbs. Put one of the left, the other right in the FX channels’ insert routing. But of course a double mono reverb hard panned l/r isn’t a mono reverb anymore 
What are you trying to achieve?
I mean what is the difference by panning here http://imgur.com/G8Uxu3m
vs
panning here Imgur: The magic of the Internet
Thanks
You can achieve more or the less the same result: panned fx.
Panning sends: the input of the inserted plugin (must have stereo input, aka ‘true stereo’) gets panned signal > the reverb tail/delay feedbacks/whatever will reflect this. Obviously you can send several signals with different pannings into it - leaving the FX-returns plain L/R and get panned FX though.
Panning returns: this way you ‘pin’ the FX into a certain position, send panning has no or just little influence.
There’s not much more to it. It’s about what result you’re after.