I usually eat with knife and fork together: I hold the fork in my left hand and the knife in my right hand.
The fork in the left hand usually either "spears" bits of food, or is held with tines horizontal so that the knife can push things onto it. (What I don't do is spear a bit of food [e.g. meat], then shovel on some other food [e.g. peas or mashed potatoes] on top—my father does this.)
If there's nothing that needs to be cut nor small things such as peas, I'll also eat with just a fork, in which case it's in my right hand.
And I've found that while I can eat with the fork in either hand, I can only comfortably use the fork in my left hand if I'm holding a knife in my right hand—even if I'm not currently using the knife! But if I lay the knife down, it becomes very weird to hold the fork in my left hand.