In general, it should be fairly easy to feel or 'palp' lymph nodes. That's what doctors usually do during a regular physical exam. What they check for includes: size, shape, texture [lumpiness], symmetry [nodes on both sides of the body should be about the same in all ways] and number [sometimes it may seem that there are more nodes than there should be.]
However, since there are other organs, glands and tissues nearby, it is best to have this evaluation performed by an expert - your doctor. For the same reason, a positive lymphoma diagnosis is usually made only after you've had blood tests [CBC Diff], diagnostic imaging [X-ray, CT scan], lumbar puncture [spinal tap] and, sometimes, a biopsy. After all, surgery, chemotherapy and radiation treatment are nothing to take lightly.