I want to poach some salmon and plan to use vegetable broth in place of white wine. Any suggestions for herbs or spices to add?

Agree with nutcakes. I would not use veg broth. Use water, and acid (like vinegar or citrus), and add aromatics. If you need more particulars, you should be able to find recipes on the web.

I wouldn't want my salmon to taste like vegetable broth, so dilute it or just use water. Add an acid, like lemon juice or vinegar since you are skipping the wine. A wedge of onion, peppercorns. Use the sauce for flavoring salmon has a lot of flavor already.

Salmon is such a wonderful fish and so versatile. It pairs with everything other answers, as well as dill, fennel, chile peppers, lemon, lime, mint mustard seeds as whole as Dijon, shallots. Pick your flavor profile and go for it. I love ChefHenry's suggestion about putting the poaching liquid in the blender.

Tarragon. Or Sorrel and garlic, once the fish is cooked, put the poaching liquid in a blender with some butter and youll have a delicious sauce, not quite, but based on the famous Troisgois brothers salmon with sorrel.

Just to add to what Daniel suggested, some lemon peel and peppercorns would be nice.

Bay leaf, thyme, onions and garlic. Rosemary.