A recent blog post by Evan Madore suggests this product as 1 of 3 alternatives to Walnut Blasting. How would this product, added to a gas tank, be any different than other additives which don't get sprayed onto the intake valves by direct injection engines like the N55?

This product will not do anything to clean intake valves if added to the fuel on a direct injection engine. In the blog article, we believe you are referencing, the technique for cleaning valves with this product was shown on a VW EA888 engine going by the Audi/VW technique used by dealers (they do not use walnut blasting like BMW). The same technique as outlined in the blog article can be used on an N55 engine. However, it's critical to note that the N55 engine has individual PCV ports in the intake inlets in the cylinder head that need to be blocked off (this applies to a chemical cleaning or walnut blasting procedure) to prevent possible blockage of these ports during the cleaning procedure. The method in manually scraping the intake valves using this cleaner is outlined in the linked video in the blog article at the around the 15-minute mark: https://youtu.be/OM0M2bQM-ag

When I added to the fuel than. Is this product will reduce engine knock.

Completely depends on why the engine is knocking. If there is a timing issue or fuel mix problem this product cannot help that issue. This product could potentially help if injectors are dirty or if valves are covered in carbon to the point it interrupts air flow. However, if the issue pertains to fuel injection the best course of action is to have the injectors tested for balance or simply replace them.

When I put this in the gas tank can I also put the fuel injector cleaner at the same Time

These products are formulated to be used on their own, mixing them will dilute the fuel chemistry and cause them to be less effective or potentially hazardous.