hello,
There should some standard way to get it. But here is a simple query that oyu can write and found out. Get all the segments from EDISEGMENT and then query the table "DD03L" with these in the TABNAME and FIELDNAME as your fieldname (ZMATNR). You will get the list of segments that have your field.
Also there is a FM IDOC_COMPLETE_SEGMENT_READ to read segment field.
Also check tables EDISDEF, EDISEG
best regards,
swanand