What type of internship should a high school student take in order to know more about psychology but especially forensic psychology?

Is there a college near you? You might be able to work as a Research Assistant for a psychology lab. That will give you a lot of good experience in what psychology experiments are actually like.

Another option, which may be especially relevant for forensic psychology (since it isn't frequently offered in colleges) is to look up the names of some forensic psychologists in your area and ask to speak with them about how they got into their field. You may also be able to "shadow" them at work, which means you can follow them through a day in their field and observe what they do.

I suggest looking towards leadership based internships that are in low-income areas. Experience in those areas are very relevant to your future in working with the justice system. Low-income areas can show you the impact of poverty, imprisonment, and the impact on families and the community. Experience like that will speak well to any hiring manager in the justice system looking for a forensic psychologist.

Like stated before, there is no ideal internship for a forensic psychologist in high school. However, if you find something you can use to gain empathy and an understanding of the impact of the judicial system, you will have a leg up.

Hope it helps!