Quite clearly no.
Clearly, lawyers will know their client is guilty in some cases.
How they would live with themselves, if their client was declared not guilty in a trial, and then committed further heinous crimes is another matter entirely.
A lawyer must retain objectivity, because one who becomes emotionally involved in a case will not last long.
Do you mean suspect his client is guilty, or knows his client is guilty?
In the former case, his job is to put up the best possible defence.
In the latter, if the client has told his lawyer he is guilty (and the lawyer has reason to believe client is telling the truth), then he must recommend a plea of guilty and argue mitigating circumstances.
And in answer to your final question, quite easily - his job is to defend. It is for the prosecution to prove their case, and if they cannot do that (given they hold most of the cards) then the client should go free.