The target of a force power, be they force sensitives or not, may resist a force power when appropriate. This resistance can be deemed appropriate by the nature of the scene, the target being a PC, the target being an important NPC, and so on. Guidance on ruling on resisting Force Powers is found in the Chapter 8: The Force. (Sidebar on page 283 of Force and Destiny). No specific mention of the Sense force power is made in this sidebar.
The text for Sense has, on the left side of its tree, the ability to Commit force dice to upgrade the difficulty of incoming attacks. This can eventually be improved to upgrade their own attack pool.
The nature of the attacks is not specified as Force, Melee, Brawl or Ranged, just that the force sensitive is attuning their senses in preparation for combat. Nothing in the small descriptions in the tree makes reference to specific types of attack; however, it should be noted that the description of the power in the body text of both control upgrades does carry a flavor of attacks being physical in nature. As such, a GM preferring to adhere to a strict interpretation of the printed word might choose to limit this ability to such attacks.
The Force user gains the ability to sense danger the moment before it strikes, allowing them to anticipate attacks and avoid incoming blows.
-Force and Destiny, Chapter 8: The Force, Sense
This power does not apply to skills in general. A force sensitive cannot upgrade the difficulty of an enemy using the pilot skill for example. They cannot upgrade the difficulty of attacks made against someone else. They can, however, upgrade the difficulty of attacks made against them.
Structured Time vs Narrative Time
Using a power like Harm on a force sensitive target with the Sense power in Structured Time means that the target does not have access to the action it would take to access Sense + the Control Upgrade necessary to sense surface thoughts or to upgrade an opponent's difficulty. Without that access, there is nothing special to be gained via Sense which could better prepare them to resist a Force Power aimed against them. As a Force Sensitive they are aware the power is incoming, and will already be able to resist. As a special target (PC, Nemesis, etc) they are able to resist. To gain this benefit, they must have already had force dice committed to the power.
Committing Force Dice
Having force dice committed to Sense with the Control upgrade which allows the force sensitive to prepare themselves for incoming attacks allows them to be in a state of readiness for attack. Any single attack targeting them may have its difficulty upgraded once. Future upgrades of duration and strength can increase the number of incoming attacks which may be upgraded, and the amount by which they are upgraded. See Chapter 8: The Force in Edge of the Empire or Force and Destiny.
In Narrative time, for an attack which does not lead into Structured time, it could be said that a power like Sense or Foresee could be the underlying reason for the target becoming aware of an attack, and taking actions to protect themselves. Likewise, force dice committed to Sense show the active intention of the force user to be ready to protect themselves from attack.
There is no text-based reason for the Basic Ability to lead to the defender being able to upgrade the attacker's difficulty, this is specifically a factor of the left-side of the tree's first Control upgrade of the power. Of course, a GM might feel the need in a specific situation to modify the difficulty.
Destiny Pool and Rolled Resources Upgrading Difficulty
Two things can be done to upgrade an opponent's difficulty on an attack. These are to spend a Destiny point, or to use the rolled resource of 1 or more Despair against the attacker after the Opposed Roll.
Why is this important?
At the end of the description of Sense in Chapter 8, there is an additional sidebar called Using Sense in the Game. It is focused on the potency of Sense and how to manage it in concert between the GM and players. While this sidebar is focused on the information-gathering aspect of Sense, it is good to remember its advice for all applications of the power. Most specifically, strong-willed characters, and certain species may be more resistant or even immune.
This is good to remember as to use a power like Harm, the attacker has two roll elements they can potentially fail when dealing with resisting powers. They have to win the Opposed Roll, and they need to generate sufficient Force Points on their Force Dice to activate the power and upgrade(s) they want. This is enough of a limiting factor to ensure that the target has a good chance for reasonable protection in line with the source material.
Further complicating this with additional steps will slow things down, introduce more opportunities for forgetfulness or error, and will reduce the frequency with which certain powers can be used. That runs counter to the intentions described for force powers and their use in the core books. Generally speaking, allowing Sense to upgrade the difficulty of force powers used offensively against the character may suit a group, or may complicate things beyond what they find fun and thrilling in a Star Wars game. The game does not come out and state a ruling for or against this application, but it does imply the power is geared toward physical combat.