There's no single answer to how many credits you need at the end of sophomore year. It completely depends on the institution you're attending (high school, college, university, etc.) and their specific credit requirements for graduation or advancement to the junior year. Some institutions might require 60 credits, others 70, and still others might use a different system entirely (like semesters or quarters).
You need to check your school's academic catalog or speak with your academic advisor to find the correct answer for *your* situation.