Hi ,
Try reading the global data inside the userexit_field_modification , as below:
field-symbol : <fs_knttp> type knttp.
data: lv_knttp type knttp.
assign ('(SAPLMEPO)EKPO-KNTTP') to <fs_knttp>.
if <fs_knttp> is assigned.
lv_knttp = <fs_knttp>.
endif.
Hope you get the value in lv_knttp.