can an unlisted company stock certificate or bond be cashed in eve though it has another person's ? how? thanks

Your question is somewhat unclear.  I presume you're speaking of a closely held company, that is one with a limited number of shareholders.  Further, presuming that one of the shareholders has either passed away, or somehow transferred his or her stock certificate to a third-party, the question then becomes how was the transfer accomplished.  If the stock certificate was properly indorsed for transfer, to your clients order, then your client can take that stock certificate to the corporate secretary and request that that certificate be retired and a new certificate be issued in your clients name.  Your client can then seek to the transfer the certificate to the company, in exchange for payment of the book value of the certificate.  If there is a stockholders agreement, of course, the certificate is probably subject to that agreement.  If that is the case, then your clients rights will be limited by the terms and provisions of that stockholders agreement.  Finally, if the corporation does not have sufficient funds to purchase back the stock certificate, or the board of directors is not inclined to permit same to occur,  your client can try to sell the certificate to some other potential, shareholder, if not otherwise limited by any stockholders agreement.