Actually, most dogs will get enough omega six from their existing dogfood if it's a decent brand, it doesn't even have to be a high end food. Some folks who cook for their dogs, (and that is usually counterproductive to good health more often than not, and folks who actually take the time to do it right really need to find a hobby besides cooking for a dog), may want to consider adding supplimental fat rich in omega 6 though. Rice Bran Oil is generally the best choice there. It has a median level of o6, a relatively high amount of monounsaturated fat, and the Gamma Oryzanol that really is one of the most amazing non-fat substances that occur in oil of any type. RBO is hypoallergenic too, which can really be a boon to dogs prone to allergy related problems.
I'm not real big on feeding dogs or cats seeds of anything, Oil is usually the best way to maximize metabolic access to the fat. I feed my two girls, Val and Pete, A fifty/fifty mixture of Flax and RBO. Both weigh about 50-60 pounds They get about 2 teaspoons apiece on their dry food, and for mutts, they are fine looking dogs who get a lot of questions and comments about their great coat condition. Same with my barn cats actually. We even have a feral cat I feed who looked real dull-coated and ratty last year when he first showed up, who shines like a freshly minted dime now, all on a mid-tier cat food.
And my horses are so shiny it's almost embarrassing, lol. (Mostly RBO with the horses)