One of the ways to know the Will of God is by open and closed doors, for where He guides, He always provides! Often this is how He gets us to do things: By closing some doors and opening others!--And we sometimes have to accept God's no in order to find His yes!
God works in mysterious ways His wonders to perform, and sometimes we're just swept along by His current, even when we don't know exactly where we're going. So we should follow His leadings and His guidance. Where He's providing open doors, He's obviously guiding! So don't bother to knock: Just walk right in!
Which way does God seem to be leading you? Where do you have an open door of service? Which direction does it seem that He is providing the way and the means? Seek and trust the Lord, and He will lead and show you the way and open the door. Don't get impatient and try to batter it down! Trying to force the situation and push your way through just won't work! Be patient and wait, and He will open the door!