grep -Ro -i refnum .

-R for recursive search
-o to show only the filename
-i for case insensitive
refnum is the text to seach
. is the path the begin the search from

the result look like:

$ grep -Ro -i refnum .
./bk/SchAI_RCSEVALUATIONLIST.xsd:REFNUM
./bk/SchAI_RCSEVALUATIONLIST.xsd:REFNUM
./SchAI_AUDIT.xsd:REFNUM
./SchAI_AUDIT.xsd:REFNUM
./SchAI_AUDPRGMAUDLIST.xsd:REFNUM
./SchAI_AUDPRGMAUDLIST.xsd:REFNUM
./SchAI_AUDPROGRAM.xsd:REFNUM
./SchAI_AUDPROGRAM.xsd:REFNUM
./SchAI_FINDING.xsd:REFNUM
./SchAI_FINDING.xsd:REFNUM
./SchAI_FINDINGLIST.xsd:REFNUM
./SchAI_FINDINGLIST.xsd:REFNUM
./SchAI_IAUDITLIST.xsd:REFNUM
./SchAI_IAUDITLIST.xsd:REFNUM
./SchAI_IAUDPROGRAMLIST.xsd:REFNUM
./SchAI_IAUDPROGRAMLIST.xsd:REFNUM
./SchAI_IPRINTJOBLIST.xsd:REFNUM
./SchAI_IPRINTJOBLIST.xsd:REFNUM