Elgato Thunderbolt™ Dock has one HDMI port.
1x HDMI 1.4 Output (up to 2560x1600 pixels resolution, HDCP compliant)
The built-in HDMI port can drive a display of your choice. Whether you’re looking for a professional-grade screen to meet your standards of color reproduction, a non-glare model to cope with reflections in your office, or a display that trumps all others in size, supported resolutions up to 2560x1600 pixels have you covered.
The resolutions and frequencies that can be used depend on both the graphics card in your Mac and the display itself.
To find the specifications of the graphics card in your Mac, you can use the links below:
Also check the user manual of your display to see what resolutions and frequencies it supports.
Once you have connected the display to the HDMI port on the Elgato Thunderbolt™ Dock, you can find out the frequencies and resolutions supported by your Mac and your display by going to System Preferences > Displays window. To view all the resolutions supported by your Mac, press the Option key and then press the Scaled option.