i think he's asking which master setting to use.
WD srives (along with some other brands I'm assuming) give directions for "master" or "master with slave"
for your WD drive, remove the jumper altogether as it will be the only drive on that "cable" (ie in the enclosure)
Most enclosures require that hard drives be set as master. some will work with the jumpers in different positions, and some might require a different jumper setting (although i'm not aware of any that do).
definitely check the documentation with the enclosure, but without knowing much about that particular enclosure my guess is to set as Master-Single (ie no jumper)