Either the generic approach for comparing two instances of any given struct type:
memcmp(&cllc2d1, &second_cllc2d, sizeof(CLLocationCoordinate2D))
or
cllc2d1.latitude == cllc2d2.latitude && cllc2d1.longitude == cllc2d2.longitude
should work, if you really want to be sure they’re exactly equal. However, given that latitude and longitude are defined as doubles, you might really want to do a “close enough” comparison:
fabs(cllc2d1.latitude - cllc2d2.latitude) <= epsilon && fabs(cllc2d1.longitude - cllc2d2.longitude) <= epsilon
where epsilon is whatever level of error you want to accept.