Dobby does not appear but is mentioned twice:

In Wizard Angst says when harry gets mad dream dobby still eats my skin every night and is identified as an elf

In Wizard Swears Dobby's name is in a wizard swear ("Dobby's sock.)

Trivia: Dobby smells like his own clothes and socks .

He is a free and stinky elf .

He and Harry are friends.

Dobby also smells like Ron .

Dobby smells like Snape, who smells like broccoli and poop.

He reveals to Harry that he works out and likes the smell of Hagrid and a smelly old man.

There is no puppet for him.

He also likes the smell a dessert that Snape had mad called Poop Pie .

Dobby also enjoys eating poop pie , sock soup , and broccoli.

In order to get himself clean, he asks Hagrid to take bath with him.

His stomach will always growl every day and night.

Whenever Dobby is hungry, he would say , "Dobby is a hungry elf !"

And finally, He eats marshmallows and socks.