20JT appears to be the internal name for the Thinkpad T470s.
I couldn't find the exact configuration that the rest of the name will refer to listed on
lenovo's website. It could be a typo or it may not be listed.
But looking at the other T470s configurations they're generally listed as supporting three independent displays and having USB-C and HDMI outputs.
It doesn't go into details as to whether there's any combination limitations but HDMI only supports one display so DisplayPort (USB-C almost always refer to DisplayPort Alternate Mode) would be the way to go.
The functionality you need for connecting multiple monitors to a displayport output is called an MST Hub. A USB-C (or thunderbolt) dock will generally incorportate that along with additional functionality like a USB hub or ethernet or sound hardware.
So you don't strictly need a dock, but its likely the simplest and cheapest solution these days.