べき means should or ought to, but it is stronger than a casual suggestion.
Use it for moral duty, social responsibility, rules, or what seems logically right. It is closer to “the right thing to do” than “it might be better to.”
Grammar: attach べき to the dictionary form of a verb, as in 行くべき（いくべき） or 考えるべき（かんがえるべき）.
With する, the formal and very common form is すべき. するべき is also used, but すべき often sounds tighter and more formal.
Be careful when using べき toward another person. Because it implies a standard of right and wrong, it can sound judgmental or bossy. It is safer for general rules, broad opinions, or self-reflection.
Do not confuse it with 〜ほうがいい, which is a softer “it would be better to…” suggestion.