This kind of queries already been asked here multiple times. Anyways, Fax can be viewed in the Online Service Web Portal (https://service.ringcentral.com) in both Messages > Sent Items and also in the Call Log as you mentioned.
If a fax transmission fails, the reason is reported in the Call Log Record's result property. It is also presented in the Service Web Portal. All the Fax question are answered here and the following link will be helpful:
ref: https://forums.developers.ringcentral.com/questions/144/fax-faq.html
So, you can verify receipt of the fax different ways via the API, Online Account Portal or in your Softphone application.