The question What percentage of Airbnb guest house do I own in 2024? this is not applicable to my situation. My son has a building on his property he allows me to rent on Airbnb.
You would say 100% if you are using 100% of the property and receiving 100% of the rental income.
It's more accurate to say that you own 0%. Your son owns 100%. He should claim the income and expenses from the property on his taxes. The money you receive is a GIFT from him, and subject to gift tax exclusion (I think $17,000 this year but you'll have to verify).
You don't own the property; you can't claim expenses on it (I'm sure he's claiming the expenses if you are not), nor should you be responsible for claiming the income on something you don't own. The income was passed on to you via private exchange.