Can you tell me when being assessed for antisocial personality, to what extent can one confess thinking/doing reckless things?

Depends: This seems a somewhat odd question. If you are asking about yourself, then you already know how willing or unwilling you are to discuss your thoughts and actions. If you are asking about someone else, it is not possible to make a general prediction. A therapy relationship based on trust and respect (may take some time) would be a prerequisite for anyone to speak openly and honestly.