Curly Dock is a great plant to eat! I eat it regularly. My dad had us kids picking it when we were just seven years old or so, along with lambs quarter and poke, when they each were in season. You are right that it's related to Rhubarb -- they are in the same family, along with buckwheat and sheep sorrel (but not the wood sorrel).

I use the youngest leaves in salads, like this one from last week. For cooking, they are too much of one flavor to eat just by themselves, I think. And they change to an olive-green color that most folks wouldn't be too excited to eat, lol. But they are great to mix with other greens, wild or from the garden. I like them in any vegetable soup - they are perfect for a Greek Lemon Soup with their slight sourness.

For cooking, if you want to see how dock compares to other greens, you might be interested in this video that shows cooking 10 different wild greens. Or this one that uses dock for making potlikker, an old-time spring tonic soup, along with some greens. Now that you know dock, you are in for some good eating!