Which god holds a shepherd's crook?
Amurru, an Amorite deity often referred to as a storm-god, is depicted on ancient cylinder seals carrying a curved object called, in Akkadian, a gamlu, which is generally interpreted as a shepherd's crook, e.g. by writers such as Henri Frankfort (in his 1939 book Cylinder Seals: A Documentary Essay on the Art and Religion of the Ancient Near East), Aïcha Rahmouni (in her 2008 book Divine Epithets in the Ugaritic Alphabetic Texts) and Joshua J. Mark (on the website Ancient.eu).
Several Egyptian gods commonly appear carrying a shepherd's crook, which, together with a flail, indicates them as royalty: the "shepherds of the people." Two of these deities, Ra and Ausar (whom the Greek called Osiris), are believed to have been among the earliest kings of Egypt.
In late Pharaonic Egypt, Ra was merged with Ausar's son and heir Heru (Horus) to form Ra-Harakhte, "Ra Who is Heru of the Two Horizons."
Here Djedkhonsuiwesankh, the daughter of a priest, makes offerings to him as he sits enthroned, carrying the crook and flail.
Perhaps the best-known deity to wield the shepherd's crook is Ausar (pictured below), the ruler of the dead and of the otherworld which they inhabited.
A very ancient god, named Andjety, from a place called Andjet in Egypt, may have been an earlier form of Ausar. He too carried a shepherd's crook.
Pan, the Greek god of flocks and shepherds, is portrayed holding a shepherd's crook.
Gaeeus, a minor Libyan sea-god who may have been a marine shepherd, also wields this implement. His name seems to mean "Gaia's" (Of the Earth).
A Phrygian vegetation deity whom the Greeks called Attis is depicted in a life-size statue of him which was found at Ostia, outside Rome. The image is holding a shepherd's crook in its left hand.
As DisturbedNeo said, in Egyptian mythology it (along with a flail) is held by pharaohs as symbols of power, and is thus held by Osiris as a "pharaoh of the dead".