Pain is an unreliable factor to depend upon in self defense. Sometimes it works, sometimes it doesn't. Between natural pain tolerance and adrenaline alone, things that would hurt like hell normally might not even register, and that is before you get into chemical effects that may or may not be in play.
(In the case of your knife attack, many survivors of stabbings have reported feeling numbness or no pain, which makes it more a common mechanism of how knives work, and why most knife arts teach "overkill" because pain is not the stopping factor.)
So, broadly, what do folks use instead?
Positioning & Structural Control
Although most people focus on the pain compliance aspect of controlling locks and grappling, the main thing is structural control - putting yourself in a position where you can apply force efficiently and the person you are controlling cannot do so.
Sometimes this is using larger/more muscles vs. a small target, sometimes moving your center of mass and centerline to efficiently use force while pulling your opponent's arm or turning their spine off center, sometimes forcing end-of-range positions where people have little strength (hammerlocks, chicken wing locks). Usually it's a combination.
The fact that they either cannot bring enough muscle in play, work against your mass, and/or would have to tear their own tendons to make it work, is the factor, not pain.
Break bone, tear muscle, destroy a joint. If it cannot mechanically perform the action, it simply doesn't work, and it doesn't matter if it hurts or not. Some strikes, grapples, takedowns, and obviously, weapons in general, aim to do this. Break a collarbone, and the arm on that side cannot lift up, regardless of whether it hurts or not.
Pretty much anything combative-focused aims to do these things, with differences in terms of what weapons are used, what level/speed of escalation is appropriate according to the situation (military vs. civilian, etc.).
Methodology, not a specific technique
So... you might read the two categories above and go, "Wait, don't MOST martial arts aim for these things?" and yes, that is correct. If you are pulling from a movement form to deal with actual fighting, you deal with positional control and/or structural damage, depending on how far the art has moved from the original goal.
Very few things are "pain only", and where they are used, they are small additions to the core fighting methodology, not a single reliance. The groin kick, "wiping" the eye with your thumb or fingers, pressing into soft tissue, are extras you add onto everything else, not things you plan on winning and escaping with.
So, obviously, the groin kick you list is unreliable in this situation. The other two techniques you list are unreliable for other reasons, and basically not the core of what I would want to depend on if someone comes at me with little or no pain registering in their head.
It's not a matter of "where is the magic off button to hit?" but rather, "What are the ways I need to move to keep myself safer, while doing the damage or restraining this person as needed?"
Utilize better positioning, control their structure appropriate to your methods, and decide what kind of damage is appropriate to the context and the quickest way to deliver it.
Edit for Knife Addition
Knives change the nature of a fight quickly. A link to an answer I had about defending against knives previously with mostly the same general principles. Knives are easy to use, but hard to defend against, which is why arts that deal with knives become very deep and complex at some level, because being "ok" at protecting yourself against them is hard.
The groin kick is now even worse of an idea, because not only is pain not going to do much, you cannot shift your position off-line from a rush while kicking, and if they catch your leg, they can cut that up too.
Both the punch and neck chop require getting past that knife to land. The solar plexus strike is unreliable in general, and now you're putting your arm in the danger zone for it. Neck chops have a shorter range than punches even, and tend to telegraph which is why they're usually part of a flurry, not an entry.
Well, as mentioned in the linked answer - control & destroy. Some styles of combative arts focus more on one or the other, but you need to make sure you're not getting cut, and that the person can't keep trying.
Control can be achieve through: catching the arm at the beginning/end of a swing, where the momentum is low, jamming the elbow or forearm, looping & locking the arm, looping & locking with cloth, or a jacket, and so on. Control is always followed with a disarm or destruction. All of these methods? Positional & structural control, as mentioned above.
Destruction is usually either: using a weapon against the weapon arm, high powered attack (elbow, knee) against a specific target (bones in hand, bicep, collarbone) to destroy the weapon arm, or a tendon tear/bone break lock. All of this? Structural damage.
Some styles recommend pummeling the head to get the person on the defense, though, admittedly, if you think the person is less susceptible to pain, that seems iffy to me.
Unfortunately, the answer to "what to do if someone comes at me with a knife?" is "learn a whole methodology to deal with it and train hard" in the same way "What to do if someone has cancer?" requires years and years of medical school and lots of expensive equipment to make treatment happen.