he is in slateport by the museum or by the ship dock toward mauville on the right
You deliver Devon's Goods to Captain Stern who is in Slateport City's museum.
Damn i wish i knew
You go to slateport and you deliver the Devon goods to captain stern.
head back to the Devon building to report mission sucsess
Give it to the guy who asked you to get the goods back in rustboro city.
After you deliver eveything for the Devon Goods president he will give you the exp. share as a thank you.
Go to Devon and talk to everyone in the place
you deliver it to captn.stern
To get the PokeNav, you have to deliver the Devon Goods to Devon, the scientist from Devon Corporation. Obtain these by beating the Team Magma Grunt in Rusturf Tunnel. Once you've done that, the president will give you the PokeNav.Note: This is for Ruby. I'm not sure if this applies to Emerald, Sapphire, or anything else.
The Devon Goods can be easily obtained after defeating the Aqua Grunt in Rusturf Tunnel.
you'll have to talk to a researcher/scientist looking guy inside the building below the museum, then he'll tell you that the professor isn't there, then you'll have to go to the museum to find the professor on the 2nd level.
you need to go to the boat warehouse in slateport and talk to the first guy you see he will tell you to go find captain stern. now you go to the museum were a whole line of aquas were blocking the door . go to the top floor of the museum and talk to the inly guy there and he'll take the goods off you and you will have to battle with two aquas. after this the route to mauville city will be open.