Converting from V-brakes to Disc Brake without existing mounting holes I have an Electric Bike with rear brakes which are not as strong as front disc brake (countless amount of tweaks never solved it well without rubbing the wheel too much).
So, I am looking at converting to disc brakes

Is it possible? Using which products?
I was thinking of a start with those two:
http://www.aliexpress.com/item/MTB-Disc-brake-flange-disc-tray-adapter-screw-thread-switch-disk-disc-tray-refires-disc-brake/32312668990.html

And since I cant post more than 2 links, search on AliExpress for "brand new hs1 brake rotors" - the one from "Store:Carbon-Bicycle Co.,Ltd" for 9$ is the one that was recommended.

But I lost contact with the guy who guided me to those once in a train, so I don't know how to proceed what else do I need...

The frame is made of aluminium, and below you can see pictures of the read wheel, to understand the construction and my options...







Note:
The question referred to: Disc brakes on leader doberman which has no tabs and adaptors

Deals with question on how to piece together parts for the specific branded Doberman frame, while in my case, I am not entirely sure which parts do I need, and my frame is Chinese generic no-brand frame, making it much more difficult to find the correct parts that would fit together well.
In general, on electric bikes, the rear hub is an essential part of the electric motor/drivetrain in order to power the bike and is very different from rear hubs on standard 'manual' bikes.

Because of this, in order to have a rear disc brake system you'd need to replace your hub (or whole wheel if this isn't possible) with one that has disc brake rotor mounts. You won't be able to use the screw on aluminium one linked to in your question.

Secondly, you'll have to install a retrofit device onto your frame to mount the disc brake caliper. These are available with vary degrees of quality but looking at your frame, you'd need to remove the pannier rack which I assume you probably don't want to do.

I think it may be fruitless to pursue this conversion to be honest and if you have a disc brake on the front of your bike this is where to majority of effective braking should be happening anyway - simple rule is that you should use the front brake to slow your bike down until the point where you can use the back brake to bring your bike to a stop.