A good general contractor. Selective demo will need to be done to see what the damage is underneath the flooring.

I recommend your friend call a water damage restoration company. A company who has the ability to evaluate the damage, cause, and provide remediation.

Likely a leaky toilet bowl wax ring. House is on a slab so the only thing likely to be effected is the flooring.

Pergo (laminate) flooring of the past was a poor choice for wet/ potentially wet locations. The Pergo in my son's house had existing water damage when he bought the house because of a leaky ice maker connection.

Correlation is not causation. Change the wax ring first please.

Thank you all!!! It does seem that Pergo was a bad choice there. I’ll have him start with replacing the wax ring and hopefully they’ll see more of what’s going on.

Your toilet was ring is either leaking or it's not. If it's not, the flooring choice matters less.

Hi,

When the leak is repaired, I would spray a light coat of bleach on the stain see what happens.

Good Luck Woodbutcher