We are using Sitecore 10 and SXA. Can we skip the Item/field validations on specific site in Multisite environment?
Short answer is no. Workflow/Validation rules follow the defined templates, so if you're using a template on multiple sites, the workflow rules will follow.
You have a few options however. You could consider setting up Field Validations using the Sitecore Rules Engine. In this setup you could make "Current Site" part of your consideration for when the validation rules should trigger.
Alternatively you could look into Custom Field Validators, that would be based on the ones Sitecore provides out of the box.
Generally speaking however, you should probably re-consider how your entire information architecture is setup if you feel you need this specific functionality.