Is the Following Train Route the Quickest From Nice to Lake Como?

I would would go to SNCF, the French railway site or to Trenitalia to check schedules and prices. Looks like the minimum time is about 6 hours.

The link timed out, but I would say Nice to Ventimiglia to Milan to Varenna in 6 1/2 hours is pretty good considering you only have to change trains twice.

Not an easy answer since we don't know where on the Lake you are staying and the departure time from Nice.

The direct IC trains from Ventimiglia to Milano C.le take 3 hours and 50 and depart at 9:10, 11:03, 15:10, 17:03 and 19:10. The fastest trains from Milano Centrale to Como S. Giovanni are the ECs headed to Switzerland and take 37 minutes. They depart every 2 hours, the first EC leaves at 9:10.

Find the time needed to go from Nice to Ventimiglia and you'll get the quickest route to Como S. Giovanni.

The German Railway's train planner gives the fastest routes by default. But the best place to book this is probably Trainline. Be aware that for Italy not all trains are already in the timetable for dates after June 11. So if you are travelling after that date wait a bit with booking.

On the website you have shown, the fastest trip I saw from Nice to Milan is a bit over 5 hrs with one change.

Where you mean by "Lake Como", means you need to add on to get to that point from Milan.