Kevin Hyden and Richard Prendergast are said to have tried to kill Whiting at HMP Wakefield on November 8, 2018.
They each face a second charge of unlawfully and maliciously wounding him with intent to cause grievous bodily harm on the same day.
Hyden, 40, appeared at Leeds Crown Court via video link from HMP Frankland in Durham.
Prendergast, 39, appeared via video link from HMP Manchester.
Both men denied the charges brought against them, meaning a trial will now take place.
A five-day trial is scheduled to begin at the court on September 7.
Judge Tom Bayliss QC told the men that they would remain in custody until their trials took place.
Whiting was already a convicted child sex offender when he abducted and murdered eight-year-old schoolgirl Sarah Payne in July 2000. He was jailed for life in 2001.