Witnesses in federal or state grand jury proceedings are not entitled to legal representation, even if the witness is the target of the investigation. A grand jury witness may choose to hire a lawyer, but lawyers are not allowed to accompany their client into the jury room.
The role of a grand jury is to determine whether or not there is enough evidence to bring a suspect to trial on criminal charges. A trial jury then determines whether or not the suspect is guilty.
The Sixth Amendment guarantees a defendant representation only in criminal proceedings.