Grognak the Barbarian is a series of comic books published by Hubris Comics in the mid-21st century. The comic books relate the adventures of the titular character in a prehistoric world.
In the sniper nest in the main hall, at the base of one of the generators. (From the central platform with burn barrel and chess board, it is the platform directly northeast. Bright lights - large generator - wooden housing. Grognak is on top of that housing.)
North-northwest of the Corvega Factory is a Sewer Grate to Drainage Tunnels. Go in, and into the room ahead to your right. Grognak is on the bookshelf straight ahead as you enter. (This is the Yankee Bravo radio signal origination point.)
West, you can get here by running through Tepid Sewers, it's on the second level of the building the super mutants are around, on a shelf with the ammunition boxs.
In an ammunition box in the burned out bus near the red railroad car. You can get the key from the random encounter "More Than Just Scrap", or you can just pick the lock (hard).
A copy will be given to you by Amata in Growing Up Fast during your birthday party. If you don't use it during this quest, it will be in the dresser in your room when you start the Escape! quest.