Normally we use 3 parts soy sauce to 2 parts rice vinegar (rough measurement of course, I like a little extra soy) and a bit of sesame oil.
We add some chile garlic sauce if we want heat. You can add fresh minced garlic if you like garlic but not the heat. And depending on the type of dumpling, you can also use a bit of fresh grated ginger.
Do the garlic. I’ve always found that scallions or green onions adda nice visual component but not much in terms of flavors. How about julienned ginger?
My two favorite chili sauces are the Huy Fong Chili Garlic Sauce (Rooster that isn’t Sriracha sauce) and Lao Gan Ma Chili Crisp Sauce (Grandma sauce).
I would combine this with 3 soy:1 chili and a splash for sesame oil.
Alternatively when I get fresh chilis from my uncle’s garden, I would dry and dice them, then pour over hot oil (neutral) infused with Chinese five-spice.
I eyeball whatever we have on hand. It’s usually soy sauce, rice vinegar, mirin and julienned or grated fresh ginger with a splash of toasted sesame oil at the end. If I have fresh small red chilis on hand, I mince them very finely and add them to the grown up sauce. The boys like it when I add a small spoonful of honey to theirs.
I use my husband’s family recipe: add soy sauce, distilled vinegar, and sugar to a jar filled halfway with minced garlic & ginger, and sliced green onions. Let sit and just keep topping it off with more of the same when it gets low. It’s all done to taste.
It’s better with age and you can add sesame oil and/or chili when you eat it. Don’t add the oil directly to the whole jar or it can go rancid.