On this Duke Nukem page you can find cheat codes, CON files, TCs, and more.
Cheat Codes:
DKROZ: God mode and unlimited Jetpack.
DNHYPER: Puts you in Steroids Mode.
DNITEMS: Gives all inventory items and keys.
DNWEAPONS: Gives all weapons and ammo.
DNKEYS: Gives all the keys.
DNSTUFF: Gives all weapons, keys,
inventory items.
DNSCOTTYxyz: Level Warp. x is Episode Number, yz is the level number.
DNSKILLx: Changes the difficulty mode to x. (x can be 0 to 3)
DNUNLOCK: Opens all doors and unlocks all locked doors.
DNMONSTERS: Turns off (or on) the monsters in the game.
DNCLIP: Walk through walls.
DNSHOWMAP: Shows the entire map.
DNCASHMAN: Spews money everywhere
when you press the space bar.
DNCOORDS: Shows extremely detailed map corrdinate/level information.
DNSKILL#: change skill level#