What welding rods for galvanized steel pipe need to be used?
Be aware that welding will vaporize the zinc in the galvanize instantly and breathing the fumes will make you feel sick. You want to limit your exposure and have increased ventilation and breathing protection. Even though you will recover if you are overexposed you won't enjoy the experience.
That said you would use the same welding rod that you would use for the base steel and the same setting and travel speed. Many groups suggest grinding back the galvanize a quarter inch or so. That reduces the fumes produced and may aid visibility. When you finish the welded area will have no galvanic protection and will be subject to corrosion. You will need to apply a protective coating to the area. I would suggest a good inorganic zinc primer. The better ones will last nearly as long as the galvanize itself.