Open up your settings either in-game by pressing Esc, or by pressing the small cog wheel in the upper-right corner of the League of Legends client.
Then, navigate to the Interface section on the left side of the Settings window. In the Combat Text subcategory, toggle on Experience Gains.
You will now see exp drops appear when you kill a minion/...
Senna, as of patch v10.20, can damage a turret outside its range with enough Absolution (passive) stacks.
Considering a turret's attack range is 750 and Senna's base attack range for Piercing Darkness (Q) is 600, it takes 120 Absolution stacks to have the same attack range of a turret and 140 to outrange it, since Senna gains 25 bonus range for every 20 ...
Ravenous Hunter is a Drain Effect, so its apply to all damage sources.
Liandry's Torment has 2 passives: Madness stacks w/ any damage you deal; Torment is applied by any Ability Damage, so if your ability deal damage to a unity torment will proc.
Yorick's ghouls do apply spell damage, so yes it works.