Make sure you have registered to the exact same account that your other Nook is registered. You can verify this in Settings under Device Info. As long as the account is the same and you are connected to WiFi, your account should sync.
If your Library has already populated but you are just waiting for them to download, they don't download on their own. Only the 5 most recent items download on registration. The rest you have to tap on individually to begin the download.
Thanks. My impatience got the best of me.