How can we test the hippocampus for damage or more specifically how can dysmnesic syndrome be diagnosed and confirmed ? apparently an eeg does not

No sure test.: Korsakoff's syndrome (dysmnesic syndrome or alcohol amnestic syndrome) can be the result of thiamine deficiency, but not always. There is no sure way to tell. Diagnosis is based on several factors. If in doubt of the diagnosis, get a second opinion. See this discussion of it here http://www.alz.org/dementia/wernicke-korsakoff-syndrome-symptoms.asp