How do I house train a 9 month old Pomeranian?

Threre is lots of good advice in this thread https://www.askmehelpdesk.com/dogs/am-wits-end-pup-646555.html Follow our dog experts advice they know their stuff! If you have more specific questions please post them.
DO NOT PUNISH THEM BY RUBBING NOSE IN MESS. That will make them fear you and is abusive!

The same way your would a puppy. It might just take a little longer.

A lot of people use puppy pads and put them by the door so if the dog has to go it can go there if it really has to (I didn't use this because I didn't want my dog going in the house at all; but it helps to get them to the door at least). Apart from that take the dog out every 3 hours and gradually increase the time between potty breaks as they get better at knowing what to do. When you go outside it helps to give a command like "go to the bathroom" so that every time you go out they know what to do. When your gone for the day or even at night it helps to crate train them because they won't go in the crate so it will help them practice to hold it and keep your floors clean.

If your dog does slip up; which happens occasionally only punish them if you catch them in the act... otherwise they won't know what they're being punished for. I used a water bottle with my german shepherd if I caught him in the act and loudly shouted no. I also would gently point his head towards the mess and say no about three times and then take him outside to finish his business.

Rewarding them when they successfully go to the bathroom outside is also important because they will associate the treat with going outside.

Hope this helps!!