Yes dogs can take aspirin for arthritis or other pain.
Just give them one aspirin per day to help with the dogs arthritis.
Don't overdose the dog and giving the dog more than 1 aspirin per day could cause an overdose in the dog unless your vet says it's okay to give the dog more than one aspirin.
For larger dogs they can take a whole aspirin and be okay with the dosage.
But for a smaller dog they should only be given half an aspirin per day for the arthritis or other pain.
Smaller dogs need less dosage than larger dogs do of aspirin and other medicines.
You may also need to crush the aspirin up and put it in the dogs food such as with canned dog food you can mix the crushed aspirin in with the canned dog food.
Some dogs will only take the aspirin or other medicine when it's mixed in with food and some will take the aspirin or other medicine directly.