Ideally all players should have a good grasp of the rules. To officiate, rule knowledge needs to be much deeper and studying FIH rules of Hockey is a must.
FIH rules of Hockey
This is also available by downloading the FIH Rules of Hockey App. Here, guidance for umpires can also be found which is essential for applying the rules.

It should be noted that Standard Adult League Regulations for East Region section 11 stipulates what level of Umpiring qualification is required at each Grade.
Further information with regard to match day administration can also be found within the regulations:
Regulations & Supporting Documents | East Hockey (englandhockey.co.uk)