Is there a way that I can find out (using a terminal cmd/util), if across an internet path that a datagram may travel, if there are routers that utilize MPLS?
You cannot really tell the path that a packet may travel or has traveled. The packet has no record of that, and the path could change from one packet to the next because routing is dynamic. Routers route packets one at a time, regardless of any packets that came before, and an Internet path can change with no notice.
traceroute to check what routers are along the route, use
w3m (or your preferred command line web browser) to find what ISPs own those routers and their contact details and then use
mutt or whatever) to get in touch with them and ask if those routes use MPLS. It's not guaranteed to work, of course; it depends on them replying to tell you.