Student or Learner
I don't understand the structure of the following sentence.
To summon, as required when exercising the above-mentioned powers and functions, persons concerned to testify or give evidence.
The comma after summon seems mis-placed to me; it should come after required.
"Persons concerned" is extremely awkward.
I would write this as follows
When exercising the above-mentioned powers and functions, you are allowed to summon, as required, the appropriate people to testify and give evidence.