“How can I tell if someone has schizophrenia?”

It depends on several factors. What type of hallucInations? Do they interfere with the person’s functioning? If this is a new thing then first you have to make sure it is not due to substance use or a medical condition (certain seizures, brain tumors and other medical conditions). Schizophrenia tends to also be associated with functional decline and other related symptoms. Your friend should see a doctor even if it is just an urgent care at first for a medical check up and lab testing.

If the hallucinations are not real in any way at all

Look at this link
https://www.nation.com/everything-you-need-to-know-about-schizophrenia/?utm_source=bing&utm_campaign=Schizophrenia-DT&utm_content=Treatment&utm_term=signs%20of%20schizophrenia&utm_medium=search&imp=48384