I'm not an expert but here is my answer:
Jenith is (a) job holder in a private company for some months. He (had left) his job in a bank for a better job (which) he was longing for a long time. His father usually told him that man (could) decline in not itme if they had a lot more pride of self, which he still remembers. One day his father advised him not to run after money only but make friends who can contribute happiness (to come) after you. Therein lies your ultimate success. The father had told him really genuine things, hadn't he? (Therefore) his words still echo in his mind. He is his superhero. If he (had listened) to his father, he wouldn't have tried changing his job rather been satisfied with it and made good friends. We know, the new job has made him (think) more about his previous job.
Step-by-step explanation:
(a)= Jenith is not the only job holder so it cannot be 'the'. Job starts with a noun so it cannot be 'an'.
(had left)= Jenith left his job in the past and is currently out of that stage as he has a new job.
(which)= 'Which' is describing a word: 'job'. If it was describing a situation or time in which he was longing for a job, then, as you can see, it would be 'in which'
(could)= It has to be past tense because 'man' uses the 'had' verb. It is 'could' because it is only a small possibility and not proven or more truthful in which case 'can' would be used.
(to come) This sentence needs 'to' in order to make sense. [it just sounds right, maybe because there is already a verb being used for it.]
(Therefore)= There is no reason his father's words wouldn't echo in his mind; in fact there is evidence for it.
(had listened)= This is used for a situation which happened before the past. Him changing his job was the first step back to the past, and him listening to his father would be before that.
(think)= 'Made' already sets it in the past, and the action 'think' is used in the same time as 'made'. If it took place before 'made' then it would be a past tense: 'thought'