There was a small window with Press x for Synergy.
So far I know about
1) Blood Fountain (Undaunted Guild Ability) Channeling where you kneel down and gain a big Health regen
2) Impale where you step on the ground and add some damage to your enemy
3) Supernova (Ultimate from Templar) that adds damage and snare to enemys
I donīt really think it is super important (yet useful) to know what the displayed synergy does. I think it is useful and beneficial in every case so Iīd always press x whenever it pops up :P
There is no universal symbol or so to show that you have triggered that synergy - you will learn when youve done it ofter enough i assume
