The purpose of the AD would be evident by the reason to put it out! Along of course with th effectivity and compliance date.
There is also the local Boeing field office rep to give an answer unless I am presuming if you are working for a company with access to a technical dept the guys would no doubt give out that info anyway!
I am speaking as an ex development engineer retired and things may have changed of course but generally having been responsible over may years for SB and AD action the reasons are always many and varied with perhaps an operator in some
cases finding in service problems which will result in SB action especially if there are FAA or CAA inputs!!