A person who studies writing can be called a linguist or a philologist, depending on the specific focus of their study. They may also be referred to as a literary scholar or a composition specialist.
Someone who studies speech is called a speech pathologist or a speech-language pathologist.
A person who studies languages is called a linguist.
A person who studies phonetics is called a phonetician. Phonetics is the branch of linguistics that deals with the sounds of speech, their production, and reception. Phoneticians examine the physical properties of speech sounds and how they are used in different languages.
A slang term for someone who studies very hard is a "grind" or a "bookworm."
A studious person is someone who is dedicated to learning and academic pursuits. They are often diligent in their studies, focused on acquiring knowledge, and committed to their education.
You call someone that studies metal a metallurgist.
A physicist.
a person who studies planets is a planetologist.
There is no special name for someone who studies Hebrew.
A numismatist.
A Zoologist
An Anthropologist.
malacologist
euclidist
Gemologists
psychologist
A Technologist. :)