I'm using a Lenovo ThinkPad X260 "20F6005HUS" with a docking station which has an Intel HD Graphics 520. I have two screens (monitors) currently connected with VGA and DVI ports, but my laptop screen is blank (doesn't display anything). Will this current setup support a 3rd screen or will I need to upgrade the graphics card/invest in a displayport addon? If addon is needed, any recommendations?
The internal screen going blank like that means that one of the two connectors is connected to the same DP stream as the internal screen. This means that you are limited to connecting only two monitors to the Intel HD Graphics engine (even though it has an unused output stream and can support three monitors).
Your only method for adding another monitor is via the addition of a secondary graphics engine. In an older laptop like this, your only option is to add a monitor via USB 3.0. There are USB-based graphics engines that can support one or two monitors. Here are some examples of USB 3.0 graphics adapters:
Hope this helps,
Already Scott pearson clearly explained with example . Now I am giving the technical specifications of HD 520