Maybe one. Usually only one lymph node can be sufficient for the pathologist to study, as all the lymph nodes in a region are expected to show similar findings. If there are more than one lymph node that are enlarged, then sometimes more are removed.
I have HAD a neck. Node biopsy, and I did not have lymphoma, but that is why I had it done! It is a very typical procedure for an ENT or general surgeon to perfom as an outpatient undder local anesthesia. Getting the node (as opposed to aspirating cells) defines the archtecture and the composition of cell by a hematopathologist. Some nodes show other things, benign and malignant.