Which possessive adjective is used with the words "human being"?
Should I say human being and his problem? Because being the word human being a neutre word, I can seem to find the right adjective.

Question

Answer

Human being = singular

Human beings = plural

A human being and his/her problems.
Human beings and their problems.

Answer

As J. Rios responded, "his or her" is necessary for this singular noun. It is awkward, but we do not want to unintentionally exclude half the human race. The solution to the problem is always to pluralize. Use "human beings", and then the possessive pronoun "their" is appropriate.