One day my local pharmacist was in a chatty mood whilst filling my request and one topic that came up was doctor's handwriting.
The answer is yes, they do (did ?) receive training in handwriting recognition.
Basically it involves learning to recognise common abbreviations and mostly being very familiar with drug names and dosing.
As the pharmacist said, when he received his training it was "easy" because the formulary was "somewhat shorter" than it is today. As a result he said his junior trainees struggle and frequently come to him guidance until they've had sufficient exposure.
However with things moving to electronic prescriptions the days of deciphering will be relic of the past for many pharmacists.