Your colleague needs to deal with this immediately! They need to keep a diary of every single incident as soon as it happens. They must notify the immediate manager and HR ASAP in writing so there's proof especially if they take the legal route. It's the employer's responsibility to investigate and take corrective action. The employer cannot punish them for reporting this.
If the employer chooses not to do anything or punishes your colleague (firing, demotion, etc.), then a possible next step would be to go to a lawyer. You need to follow up with the employer and give them enough time to correct the bad behavior. If an employer is dumb enough to punish or fire the colleague for reporting harassment, then it could be seen as a constructive dismissal or a human rights violation and that could equal to severance.