I am a fresh graduate with a degree of BS computer engineering. I want to be in the field of information security. What position should I apply to be in this field? Thank you!
Job titles tend to be a bit unreliable. I'd do a search for "security", then read over the resulting job postings' descriptions to see if they fit what you want to do. And when you contact the company, be explicit about your interests, so they can quickly tell you whether this is a good position for you or not without wasting either their time or yours.
Pentesting is a wide area that requires a not just a specific field, but one that is most important is software engineering.
most important areas include: networking, cryptography, reverse engineering, system programing and coding in general.
In particular any field that will help you master above areas in assembly and C/C++ will give you a good start.
being able to code in many programing languages is a big advantage in pentesting but often not enough... being able to "hunt for bugs" in existing applications, is what is required skill for any pentester.