You can chain as many of these panels together as you d like when tiled separetely from the Arduino. For the second panel, connect the DIN connection to the first panel s DOUT, connect the ground pins together and power with 5V.
This WS2812 Pixel Matrix Shield is equipped with 40 WS2812 RGB LEDs arranged in a 5×8 matrix. The shield is powered by the 5V onboard Arduino supply. An external power source of 4 to 6V may be required if you are planning on lighting all the pixel at once at full power