Your sentence is in the present tense (I would ask Bob) so the conditional knew is consistent.
If your sentence was in the past perfect (I would have asked Bob) then you would need the past perfect conditional if I had known him.
In the first case the condition relates to a situation existing at the present time, you need the money now and you are discussing ways to obtain it. In the second case you are discussing a situation which existed in the past. You needed the money last week, last month or thirty years ago but circumstances have changed. In that case you are discussing options you had then but your options were different at that time.
Note that you might have got to know Bob more recently and, if you needed money now you might well ask him to lend it to you but if you were discussing a need for money before you met Bob then, at that time, you couldn't ask him.
A paragragh expressing this might be:
If we wanted to buy a car now I would ask Bob to lend us the money. I would have asked him two years ago if I had known him but I only met him six months ago.
Note that the condtional in the first sentence of the paragraph (If we wanted) is in the present but that the verb wanted is in the simple past. This is the same as the sentence in your question except that the time frame in that case is set before the conditional appears (I would ask Bob) so the verb in the conditional has to be in the simple past form (if I knew him) to match.
In short you need option A in the situation given in your question.