Which type of smoke is placed on or near the threat to suppress threat observers?

Obscuring smoke is specifically designed to create a visual barrier that helps to suppress the observation capabilities of enemy forces. This type of smoke is typically used to reduce visibility and hinder the effectiveness of threat observers, allowing friendly forces to maneuver without being seen or targeted. By deploying obscuring smoke on or near the threat, it effectively masks movement and positions, thus reducing the enemy's ability to effectively engage with accurate fire.

Additionally, while other types of smoke may serve different purposes, such as screening or masking, their primary functions differ somewhat from that of obscuring smoke. For instance, screening smoke is often used to protect assets or personnel by creating a smoke screen in a wider area rather than directly targeting observer suppression. Deception smoke is used to mislead or confuse the enemy regarding the location of friendly forces. Masking smoke can obscure a specific location but may not necessarily be used for suppressing enemy observation in the same effective manner as obscuring smoke.

Therefore, in the context of suppressing threat observers, obscuring smoke is the most appropriate choice.