WCS is the way to go, maybe you mean that you cannot read the output from its binary form? Try using the GML version then, this is an example request returning a 2x2 grid of values in GML format:

http://demo.geo-solutions.it/geoserver/wcs?service=WCS&version=2.0.0&request=GetCoverage&coverageId=nurc:Arc_Sample&format=application/gml%2Bxml&subset=Lat(40,41)&subset=Long(40,41)

WCS is the way to go, maybe you mean that you cannot read the output from its binary form? Try using the GML version then, this is an example request returning a 2x2 grid of values in GML format:

http://demo.geo-solutions.it/geoserver/wcs?service=WCS&version=2.0.0&request=GetCoverage&coverageId=nurc:Arc_Sample&format=application/gml%2Bxml&subset=Lat(40,41)&subset=Long(40,41)

For more information about the protocol, see the official spec documents: http://www.opengeospatial.org/standards/wcs

and in particular the KVP one: https://portal.opengeospatial.org/files/09-147r3