Second Ethernet port

I purchased MyCloud PR4100. This device has 2 Ethernet ports.
Can I connect it to two different sub-networks ? For example to 192.168.0.X and 192.168.1.X.

You need to look at this information, http://www.mycloud.com/learn/?id=MyCloudPR4100 , also it may help if you post your question/questions in the PR4100 subforum…

https://community.wd.com/c/network-attached-storage/wd-pro-series

Your question would be more appropriate in the dedicated WD Pro series subforum. This subforum (My Cloud) is generally for the single bay/single drive My Cloud device.

https://community.wd.com/c/network-attached-storage/wd-pro-series

Also, details of usage for the 2nd ethernet port are given in the user’s manual.

In Network Services - You have to turn off Link Aggregation. Then the second NIC will appear.
There is nothing in the documentation about this.