What is the ruling of the Sharia concerning the division of the inheritance of a man who died and has no known heirs other than his wife and daughter, after it became impossible to find his 'asaba (agnatic relatives), and is it permissible to suffice with a certificate of inheritance for the wife and daughter only?

Your sister needs to make an inheritance announcement. If no claimant to the inheritance appears after the announcement, she should refer the matter to the Sharia court to rule on the distribution of the inheritance. Then she takes one-eighth, and the daughter takes the remainder by fard (prescribed share) and radd (return). It is not permissible for her to distribute the inheritance before that. If she is in another country, she should appoint someone to handle this in her husband's country. Most likely, the husband will have asabah (agnatic heirs) if his family is large.