You should read any academic paper about eeg and bci. That would at least give you an idea of the amount of effort and what type of result/information you can expect.

As for your friend you should probably provide emotional and mental support rather than technical.

No, nobody can read thoughts. Brains don't transmit anything, and even with electrodes strapped onto your head other people can only roughly tell which region of the brain is more active than normal. They might be able to tell if you are thinking about language or processing visual stimuli. It is really that vague.
Psychiatric disorders are well known. The brain alerts you about something relevant to you, and sometimes it triggers false alarms, sometimes very often. Like listening to the TV and thinking "that was meant for me". I met a guy who smoked a lot of very strong cannabis, and he said things like that happened. He also thought he was the illegitimate child of an important Australian politician. Realistically, no secret agency is going to be interested in an unimportant beach bum, or some average school kid. Your friend should see a doctor who can refer him to a psychiatrist.

I very recently saw this book https://www.amazon.com/Battle-Your-Brain-Defending-Neurotechnology/dp/1250272955 that was making a claim this technology does exist. Haven't had a chance to read the book yet but it's on my shopping list.

While I doubt such technology exists, let's just assume for a moment it does.

Is your friend really important enough for a state actor even considering wasting their time with them? Would they really risk their super secret technology being discovered and becoming useless for influencing foreign heads of state or agents?

Or is he just a random teenager that is very unlikely to end up in the history books any time soon? And even if he not what are the chances of him actually be targeted over the dozen other reasons that can explain these (very vaguely described) symptoms that all are happening in the thousands every day?

Even after many years studying conspiracy stuff, I doubt there is anything capable of non-contact mind reading. Even direct brain implants are still barely able to interpret the most basic of thoughts. And there are probably fewer resources devoted to developing mind reading these days because such a large percentage of people are dumb enough to post all their thoughts to social media and place wiretaps (Siri/Alexa/etc.) in their home voluntarily. Plus google ad network does a good job of reading your mind by your internet browsing patterns (that is a privacy battle that I think needs more attention).

What you are describing sounds like psychotic features. This could be the onset of a psychiatric condition or something as mundane as prolonged sleep deprivation. Get it checked out by a trusted professional, don't start drawing your own conclusions.

No, this technology does not exist. Your friend may be suffering from what psychiatry defines as "thought broadcasting" and related disorders, typically in the realm of paranoid personality disorder, OCD, and possibly even paranoid schizophrenia. It can progress into the person believing that they are a "targeted individual", of which there are several cases in the psych literature of people ending their lives due to the feeling of being relentless attacked and pursued by shadowy organizations (usually three-letter government agencies). I would suggest that your friend speak to a trusted school counselor about their experience, who will be able to help them put the experience in context and refer them to a specialist if necessary. Do not ridicule them for their beliefs, but do not encourage them either. Simply suggest that since you are both school age, you need a trained professional's help and school counselor is the most accessible. I hope this helps.

That's what they want you to think, man ( ͡° ͜ʖ ͡°)