Is a Muslim's prayer unacceptable if he does not obtain his employer's permission, or if a non-mahram sees him while praying, or if he prays near someone listening to music or uttering curses?

Prayer is obligatory at its prescribed time, and the employer's permission is not a condition for it. There is no harm in performing it without his permission, as obedience to Allah takes precedence. If you pray in the presence of non-mahrams, your prayer is valid as long as you are veiled and cover your entire body, including your face and hands. Care should be taken to avoid mixed-gender environments. Hearing music or curses during prayer does not affect its validity as long as you are able to perform its pillars and obligations, but it is preferable to avoid such reprehensible acts. It is permissible to pray near your office if you are able to perform the pillars and obligations of prayer.