This game has been updated since the other guides were written in 2017 and this achievement is just
slightly easier. ANY General can spawn at ANY anchor/dolmen now:
There are 16 generals which you can see listed in your Journal->Exploration->Dark Anchors section. Unfortunately, these Generals do not spawn at every anchor/dolmen every time so may the odds be ever in your favor. I would recommend working toward the other achievement Anchor's Away to make this feel like less of a grind
After completing all 100 anchors, I would suggest heading to the Alik'r Desert (Daggerfall area south of Stormhaven.) All three anchors here are very close together and can be chained together by riding/traveling in a circle. In addition, this is a common grind spot for XP, so the anchors will be closed super quickly by the big mob rotating with you.
If you find that you only have a couple more Generals left and are not having any RNG luck in Alik'r, head back to Stormhaven and find a less populated anchor. In the new update, when a General spawns, it takes into consideration what Generals the folks attacking the anchor need. Therefore, a less populated anchor will increase your odds of getting the desired General.