Yes, you can connect more than one Elgato Thunderbolt™ Dock together, using the Thunderbolt™ ports.
However, this does not mean that you can necessarily use all of the available inputs effectively.
For example, connecting two Elgato Thunderbolt™ Docks together will give you six USB 3.0 ports, but the available bandwidth per port will be reduced significantly if you use many USB devices at once.
Multiple Displays Via Two Thunderbolt™ Docks
Connecting more than one Elgato Thunderbolt™ Dock together may let you use certain combinations of multiple displays
See this article for more information: