If a Cocker spaniel is exposed to cats from a young age then the dog and cat will play and get along fine.
An older dog that is not used to cats may need longer to get along with the cat but, with a little time and patience things will work out.
Cockers enjoy the company of other animals and will happily play with a cat.
From my own experience having had cats and spaniels, the two species get along well with the cat often joining the dogs on walks and garden based adventures.