Pilatus PC-21
This aircraft can be regarded as the turboprop trainer 2.0. It has an even better performance than the previous Pilatus trainers, in particular the PC-9. Now, student pilots can learn the majority of their flying skills in a single aircraft, before transitioning to a jet.
The PC-21 retains the basic layout of most turboprop trainers. Key features are the high fuselage with a two-piece canopy, a shark-like top of the vertical stabiliser, small ventral fin, trailing link main landing gear, bent up wingtips (not really winglets), propeller with five blades and a bigger prop spinner, giving the nose even more a shark-like appearance than similar aircraft.
The tail also makes the PC-21 look like a shark: the back end of the vertical tail is slightly pointing up, like a shark's fin. The bent-up wingtips are visible as well.
Confusion possible with
PZL130 Orlik
The PZL130, in particular the TC-II version, has many characteristics of the PC-21. If you look well you see that the leading edge of the fin is more an S shape than on the PC-21. Also the wing tips are more bent up, more like winglets.
TAI Hürkuş
The Hürkus has a similar high fuselage as the PC-21. However, it has small winglets (on most versions at least) to make identification from the PC-21 easy. Otherwise it is the bigger dorsal fin, like that of the PC-9M.
Pilatus PC-9
The PC-9 heritage in the PC-21 is clear, but there are many differences. The easiest onces are the prop with four or five blades, wings without and with continuous dihedral and top of vertical stabiliser.
Beech T-6 Texan II
Being derived from the Pilatus PC-9 it is logical that it share a lot of similarities with the Texan II. Hence the same differences compared to the PC-21 are applicable. Furthermore, the T-6 has a three-piece canopy.
KAI KT-1 Woong-Bee
This Korean aircraft more resembles the PC-9 than the PC-21. However, the wings have dihedral along the full span and the nose gear doors are shorter.
Embraer (Super) Tucano
Especially the Shorts Tucano has a similar canopy as the PC-21, which may confuse you. However, all Tucano's have a nose gear that is close to the prop, much closer than the other aircraft mentioned here.