What is the ruling on knocking on wood or asking to hold it upon receiving a blessing?

This act violates what Allah has legislated. Allah has commanded His servants to be grateful for His blessings and to acknowledge them, so that this may be a cause for increasing their submission and obedience. Allah the Almighty said: "So remember the favors of Allah that you may succeed," and "So eat of what Allah has provided for you [as] lawful and good, and be grateful for the favor of Allah, if it is [indeed] Him that you worship," and "Thus He completes His favor upon you that you might submit [to Him]."