Click on the recipe book next to Broosha and scribe Makin Stuf Da Grobb Way which gets placed in your inventory. This only needs to be done the first time you do one of the Goodies for Grobb quests, as you will get all of the recipes needed.
Collect the material you will need in Grobb, specifically:
5 mud-caked lumber, which can be collected from fallen lumber which can be found underneath trees in Grobb ( -252, -82, -895 ) Copy/waypoint -251.93, -82.21, -895.37
can also be found in the swamp outside Grobb, e.g. around ( -205, -83, -421 ) Copy/waypoint -204.50, -83.16, -420.62
15 swamp-smooth pebbles, which can be collected from stones found on the platform of Zubzub around ( -445, -76, -909 ) Copy/waypoint -445, -76, -909 or along the wall near ( -400, -60, -1083 ) Copy/waypoint -400, -60, -1083 or near the wall behind the bank at ( -495, -64, -1035 ) Copy/waypoint -495.07, -63.60, -1035.02.
10 congealed goo, which can be collected from slimy slugs found in a small aqueduct in Grobb around ( -444, -72, -964 ) Copy/waypoint -444, -72, -964.