a lawyer that is fomiliar with a case can be asked to testify befor a court of a prior clients testimoney?

If a lawyer has personal knowledge of relevant unprivileged information about a case, he can be compelled to testify just like anyone else.  It is unclear to me, however, what you want the lawyer to testify to.  Generally, attorneys' don't have personal knowledge of hte facts of the case, they only  know what has  been communicated to them by others, which in general would be inadmissible hearsay and/or protected from disclosure by the attorney/client privilege.