Lymph node biopsy? For every type of cancer, is it standard to do a lyph node biopsy? What does it typically detect?

Only in some. Lymph nodes can be thought of as filters in the body. Nodes can sometimes "catch" cancer cells as they begin to spread outside the organ or tissue where the cancer started. A node biopsy looks for cancer cells trapped and growing in a node. For some, but not all, kinds of cancer, a lymph node biopsy is necessary to determine the stage of the disease and appropriate treatment.
No. No, its not standard to do a lymph node biopsy for every type of cancer. But if a lymph node biopsy has been recommended, it can be for many reasons: 1) determine the type of cancer cell 2) determine if the lymph node is involved with cancer which can dictate staging which in turn can dictate prognosis and treatment strategies.
It . It is not "standard" to do a lymph node biopsy for every type of cancer. A cancer may be diagnosed after having spread to a lymph node from a distant site, e.g. From a lung or stomach. When cancer therapy is possible by a surgical procedure, i.e. It has not spread to surrounding structures from the organ in which it has arisen, it is standard procedure to surgically remove lymph nodes in the region of the cancer to determine if the cancer has spread to the adjacent lymph nodes. The presence or absence of the cancer in these lymph nodes is then used to determine what kind of additional therapy is necessary to aid in "cure" of the cancer. Additional forms of therapy are chemotherapy (anti-cancer drugs) and radiation (x-ray therapy).