You can check the bandwidth usage of each website from WHM and following are the steps:
Step 1: Login to WHM.
Step 2: Click on Account information on home page.
Step 3: Click on View Bandwidth Usage, here you can check the bandwidth usage of each website.
In case you wish to check the bandwidth usage of entire VPS in SolusVM, follow the below mentioned steps:
Step 1: Login to VPS Management portal - Solus VM.
Step 2: We can see the VPS name under Hostname and its usage under Bandwidth. It will show the entire bandwidth usage of the VPS.