Mesmer skills

When is the time you click on the mesmer skill to interupt the foe action? Is it when you see under there name there using a skill or sometime before that?

when u see the icon appearing when u target him... when u'r spell is casted if his icon is appearing or already there still, that spell is GONE

The best way to interuppt is to know your enemy and the casting times of thier spells.
I.E. its a waste of time and energy to try and interuppt something like an orison of healing because it casts so quickly. However some prefer Arcane conundrum or migrane which lenghtens the casting time of your enemies spells thus allowing you easier time interuppting thier spells.

So when i see mob name, and under that appears Reversal Of Fortune, then I immediately click on the mesmer interuption skill to make sure he didnt successfully cast RoF?

actually reversal is the hardest monk skill to interrupt as they cast it so fast... u goota comapre the casting times and do the calculations in your mind to find the right moment. i would recommend backfire for reversal of fortune... it works jut fine trust... use a backfire so as he will try to cast reversal so many times back to back he will get hit back to back like 96hp everytime which means a sudden death

yes but again RoF is a very quick casting time and will be hard to interupt unless you slow them down.