Sticky Grenades and Throwing knives are only available in short range battles.
A Sticky Grenade will attach to an enemy and explode which also deals massive damage to nearby enemies.
A Throwing knife will silently take out an enemy without alerting the rest of the enemies around.
These can be used by tapping either of the icons for Grenades or Knives, once selected you will see potential targets that can be attacked, tap on the target to use the Grenade/Knife (Ref screenshot below):
