Donatello famously wields a bo staff in the Teenage Mutant Ninja Turtles - and there's likely a reason Splinter trained him in this weapon. The Teenage Mutant Ninja Turtles consider themselves the world's most fearsome foursome, battling against their enemies with skill and efficiency. Splinter has given each Turtle a different weapon, rightly realizing that a mismatched combination is very difficult for an opponent to counter.
Donatello has the bo staff, the simplest of all the Turtles' weapons. The bo staff is an ancient Japanese weapon, originating from Okinawa, where it was used as an alternative to other weapons. Emperor Sho Shin banned all weapons in 1477, but this proved impractical when the Shimanzu clan invaded in the 17th century. Farmers used farming tools as weapons to defend themselves, and thus the bo staff was born. In the hands of a master, the bo staff is a devastatingly effective weapon.
There can be little doubt the creative Donatello is such a master, using his bo staff as both an offensive and defensive tool. He's able to use the staff to block most attacks - even "catching" shuriken with it on some occasions - and at the same time he knows how to sweep his enemies off their feet or incapacitate them with a single blow. However, the real genius of this weapon choice is that the bo staff serves to balance Donatello's natural character. As the Turtles' resident genius and technological wunderkind, it's easy for Donatello to become focused on more sophisticated tools, failing to realize basic ones can be just as effective. It's appropriate, then, that Splinter gave him a simple piece of wood as a weapon.
The staff can be read as the perfect challenge to Donatello's outlook, pushing him to master a simple tool rather than depending on a thousand complicated gadgets which may not perform as expected. While Donatello's genius has helped the Turtles countless times, he's always forced to come back to the same, simple weapon when it matters, grounding him in something sturdier than his inventor's instincts might have chosen. This reading is particularly interesting because it may not have been totally successful, with Donatello modifying his staff in a way most experts wouldn't advise.
Donatello tends to wrap his staff in grip tape, which most experts consider superfluous - and which may indicate a lack of confidence in his own abilities. Grip tape is unhelpful for palm spins, or for switching between striking and flourishing at speed. Ironically, it's possible Donatello overthought the bo staff, customizing it with grip tape while he was training, and never realizing it generates resistance as he slides his hands down the staff.
Alternatively, this could be read as Donatello smartly modifying the weapon for his person use, having found certain moves impossible to do with his three fingers. Like all the Teenage Mutant Ninja Turtles, he'll have needed to adapt the traditional forms to suit his unusual grip - not least because his fingers are thicker. The grip tape may well be used to compensate for his three fingers, and he may simply use the bo staff in a different way to any other combatant. Whatever the explanation, Donatello's weapon can be read as communicating his character in some fascinating ways, as with all his brothers in the Teenage Mutant Ninja Turtles.