You have to use the gmail ID and password, which was used when setting up the device for the first time. If you forgot the Password or ID, then try this process:
Shutdown your Karbonn K9 android phone, press Home+volume up+power keys simultaniously until your device boot into a completely new screen (called as recovery mode).
Use volume keys to move up and down and use home key for the selection. Now select Wipe data/factory reset and confirm it by pressing Yes. After few seconds your mobile will be rebooted and voila, your device unlocked. This process will delete all your apps installed as well as settings. Your images/videos/music will still remain in the memory card.