How to have a Request Quote only for selected items?

You can have a Request Quote only for selected items in the NP Quote Request WooCommerce plugin. 

Navigate to WooCommerce->settings->RFQ Toolkit->general tab and choose “Normal checkout” in option 1.

Setup a product as a quote item:

Navigate to product advanced setup and check the following as shown below and save.

The setup shows as below in the shop and single product pages.