What is the meaning of this drill notation on datasheet PCB drawing?
0.89mm = 0.035 inches.  4 PLC means in 4 places, that is, there are 4 such holes.  The box around the 3.43 dimension indicates that this is a basic dimension, that is, the ideal position of the hole. The Z, Y, and X are the primary, secondary and tertiary datums that the basic dimensions are referenced to.  The cross-hairs looking symbol in the box below the hole dimension means this is a position tolerance for the location of the hole. The center of the actual hole has to lie within a 0.1mm circle that is located at the "true" position.  The M in the circle means that the position tolerance is for the hole at "maximum material condition" which for a hole means it is on the small side of the allowable diameter (0.81mm in this case).  If the actual hole is bigger, then that much extra is allowed on the position tolerance.