For NQS, is it possible to know the Network Quality between Customer Site and the ISP? Without installing a probe at ISP Datacenter.

No, NQS can only be calculated between two Sinefa Probes so you would need to install a probe in ISP site to get that information. 

For NQS to work, it will require probe at both ends of the traffic, such as
Branch A – Branch B
Branch A – Public Probe

This is because it uses a proprietary protocol that was sent between the Sinefa Probes. https://community.sinefa.com/hc/en-us/articles/201113027-Setup-Capacity-and-Quality

Currently Sinefa is also in progress of rolling out more public probes for this purpose. To understand how you can add a public probe.