How does one obtain Inquisition Points in Dragon Age Inquisition?

Those are called Inquisition Perks. You get one new Perk every time your influence bar fills up and reaches a new level.

The main way to get more influence to fill your bar and gain perks is to complete missions. More important missions will gain you more influence than smaller missions. Finding new agents throughout Thedas will also gain you a decent amount of influence. Some advisor missions will also reward you with a bit of influence.

Kareen's answer is true in theory, but it is not a very good way to farm influence. A far better way to get influence fast is to farm gold in whatever method you prefer (killing giants in Emerald Graves for example) and then buying influence tomes from the merchant in Skyhold.

These give massive amounts of influence upon being bought, and unlike missions, can be repeated up to 10 times per tome.