Dan hit it on the head. Just put in the parcel number if you have it, or the address if you do not and good luck to you. If you are not sure where the line is and the neighbor is friendly and has been there longer then you, just try talking with him and see if he knows. Otherwise, you will have to have it surveyed to know exactly where it is.
You can go to the county website to get an overview of your property parcel shape and an approximation of your line. If you need to know exactly for building a fence or expanding your home, you will need a professional survey. To view your parcel go to http://www.spokanecounty.org/pubpadal/
I hope that is helpful.