I almost always put it in boiling water. Usually speaking, the more boiling water you have the better because that means the water won’t get too cold after you put in the frozen dumplings and will get back to boil faster.
You certainly do not need to use stock/broth for cooking the dumplings. Even if you want to serve them in broth, you do it after, not during the boiling.
In term of the technique, there we have very different technique for different dumplings. In some cases, you would cook the dumplings in boiling water until 80% cooked, then you turn down/off the heat and allow the residual heat to finish.
