My upstairs bathroom is above my bedroom where I have a bathroom as well. My toilet is bubbling when I use my bathroom sink & when the shower is used upstairs. & vice versa. When the toilet is flush the sink bubbles up water

You have a partial clog in the drainage line. Let me explain what's happening. You flush the upstairs john, The discharge picks up speed and bangs into the partial clog in the line and starts to rebound back pushing a bubble of air ahead of it. This is what you see in the f toilet. Then, because it's not completely blocked the discharge drains away before anything overflows. This can only get worse. The drainage line that services the toilet needs to be snaked out or if you're on a septic tank it should be checked to see if it needs to be pumped. Hope this helps and thank you for rating my reply. Tom

Where is the drainage line located & will I be able to snake it myself or do I need to call a plumber. If so about how much will that cost?

This is a job that the homeowner can do by himself. You have choices. You can snake from several places. You may pull the toilet and snake the drain line from there or go on the roof and snake from the lavatory roof vent. Put out enough snake to reach the base and 15 feet more. If you call it plumber. You should be just much more than a service call . Good luck, Tom