What receiver is appropriate for studying compromising emanations in 2019?
You use a receiver intended for use as a "software defined radio" and back it up with some software.

The software you need is called TempestSDR.

That combination of software and the recommended hardware can pick up emissions from an LCD monitor and show on your screen what the remote monitor is displaying.

This image from the rtl-sdr article shows the software in operation:



The "entry bar" is pretty low:  a bit of hardware for maybe a thousand bucks, and some free software, and you're in business.

From what I gather, many SDR receivers are usable.  For any kind of range, you'll need a high gain, directional antenna.  The example images were made with the receivers' built in antennas with each receiver nearly touching the "remote" monitor.