For gold and medals, you gain the percentage of the full rewards that your progress in the base is - e.g. a 68% raid will give you approximately 68% of full gold and trophies.
For trophies, it is a bit different, as you can also lose trophies. 0% in a battle = maximum trophy loss; 100% = maximum trophy gain. Everything in between is just somewhere between those amounts as well, like 68% is “68% on the way from maximum possible trophy loss to maximum possible trophy win for that raid”. Now, if the maximum gain is higher than the loss as your enemy is considered a lot stronger than you, then you can even gain trophies with a relatively low percentage on your attack.