Høiby, 29, faces a total of 38 charges, including several counts of rape as classified by Norwegian law in a case that has drawn massive international attention.
Høiby is set to be questioned further about the alleged incident on Thursday, the third day of court proceedings, the Norwegian newspaper Verdens Gang said.
The court heard evidence on Wednesday relating to an incident in December 2018 at the residence of Norway's crown prince and princess.
According to the indictment, Høiby is accused of sexually penetrating a woman with his finger while she slept during a party at the residence. Video recordings, allegedly made by Høiby himself, showed the incident.
The alleged victim, identified only as "the woman from the party" in Norwegian media, told the court she experienced a complete blackout and felt "betrayal and a shock" when she was made aware of the incident.
Police officers, friends of the involved parties and former security guards are also expected to give their statements during the trial.
Høiby denied the rape and serious sexual abuse allegations at the start of the trial and said on Thursday that he googled his name and the word "rape" after reading rumours about him online.
Norwegian media reported that he told the court: "I am incredibly tired today. I sit in my cell a lot and think."
Just two days ahead of the trial, Høiby was arrested and taken into custody on Sunday evening on suspicion of physical assault, threatening someone with a knife and violating a restraining order.
He has admitted to other offences, including domestic violence, damage to property, drug abuse and traffic violations. He is charged with a total of 38 counts, including four of rape.
On Wednesday, on his first day on the witness stand, Hoiby said it was very difficult for him to give testimony.
"It is very difficult for me to speak in front of so many people. I have been surrounded by the press since I was three. I have been harassed ever since," he said, breaking down in tears.
After a moment, he said he had received "heavy medication" and said he would try to do as much as he could.
"I am known as the son of Mummy," he said, referring to Mette-Marit.
"Which means I have an extreme need for affirmation," he said.
"A lot of sex, a lot of alcohol.
"Few can relate to the life I have led. A lot of parties, alcohol, some drugs," he said.
Mette-Marit's son from a previous relationship before she married Crown Prince Haakon and he is not an official member of the Norwegian royal household.
Haakon and Mette-Marit have said they will not attend the trial and do not wish to comment on it.
Hoiby's trial is scheduled to run until March 19.
The trial comes at a time of multiple challenges for the royal family, in addition to the ongoing scrutiny of Mette-Marit over her ties to the late sex offender Jeffrey Epstein.
The royal palace told Reuters that Mette-Marit had postponed until further notice a planned private trip abroad, without providing further details.
with DPA
--------------
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
