ISA 310 Knowledge of the Business was one of the International Standards on Auditing.
It is no longer effective with the introduction of ISA 315 'Identifying and assessing the risks of material misstatement through understanding the entity and its environment' and ISA 330 'The auditor's responses to assessed risks'.
It served to expect the auditors are to have necessary knowledge of the client's business.
Even before accepting the audit job, auditor has to make sure if you have sufficient knowledge to perform the audit professionally.
ISA 310 points out that the sources of auditors' knowledge are: