Hard disk reader for MacBook Pro 2017 (A1708)?

2017 MacBooks have a soldered SSD to the logic board and it is not re-moveable so I am not sure what you mean by a hard disc reader. If you need to access the internal SSD of your MacBook if it has some issue then I guess you need to try in Target Mode but you will need another MacBook to do so and the correct Thunderbolt cable to connect them together with.

Any External HDD or SSD will be readable & writable by your system providing it is formatted correctly. You will likely need a USB Type-C adapter to use with the external drive. Hope that helped.

While the A1708 does have a removable SSD module so one could in theory take it out and plug it into a case if there was one, Apple’s default encryption of the drives contents based on the given systems logic makes recovery of the files just impossible (unless it was disabled).

There is only a few ways to off-load the data either via iCloud or running Target Disk Mode to a second Mac system using the same User ID or using the original Configurator tool which was intended to allow businesses and schools a way to duplicate a given configuration across multiple systems which also had a master Admin account across them. Otherwise is using an external drive to copy the stuff off.

Not maintaining a good backup of your stuff in some form is needed before disaster strikes, sorry