So im thinking about getting a puppy soon (in a few months) but my brother has a dog already and she has been an only dog since he got her 3 years ago. His dog is a shiba inu and When i read about that breed it says they can be aggressive but I dont know if she is aggressive or not since she has never been around another dog (that i know of). A few months ago i introduced her to my friends puppy but we only let her sniff it and she SEEMED fine but then again my friend only stayed for 5 minutes. My brothers dog can be aggressive with my cats though if she is eating or has a bone.

My question is, how can i properly introduce my new puppy to my brothers dog when i dont know if his dog is aggressive or not?