After in game testing:

Any extinguishing of a teammate by non-Medic action: via Jarate, Mad Milk, Dispenser, or air blast.

of a teammate by non-Medic action: via Jarate, Mad Milk, Dispenser, or air blast. Destroying sappers using the Homewrecker as Pyro

using the Homewrecker as Pyro Destroying sappers on friendly buildings other than your own as Engineer

on friendly buildings as Engineer Killing a Medic actively healing an opposing player as Scout

actively healing an opposing player as Scout Stunning a player with Sandman is 1 bonus point. Moon-shot stuns (long distance) are worth 2 bonus points.

a player with Sandman is 1 bonus point. Moon-shot stuns (long distance) are worth 2 bonus points. Healing teammates with tossed Sandvich/edible . This is the act of them picking it up, you do not receive healing points.

. This is the act of them picking it up, you do not receive healing points. 2 Headshots with the Huntsman grants 1 bonus point as sniper.

If you have damage indication turned on (Advanced → Show damage as a number over players) you will know you gained a bonus point when a purple "+1" (or "+2") appears on the player or teammate that let you gain it.

All other points go towards their respective categories. Cart pushes are added to capture point totals. All backstab and headshot bonuses go to kills. All direct or indirect healing goes towards healing @ 1 per 600HP healed.

With the rate Valve adds user content to the game, I am unsure if any of the newer weapons grant bonus points upon successful use, but it appears that bonus points are essentially granted for selfless team-centric acts.