Possibly

In the foreword to Lord of the RingsThe Lord of the Rings, Tolkien observes:

Saruman, failing to get possession of the Ring, would in the confusion and treacheries of the time have found in Mordor the missing links in his own researches into Ring-lore, and before long he would have made a Great Ring of his own with which to challenge the self-styled Ruler of Middle-earth.

Tolkien therefore definitely conceives of Saruman as being capable of making a Ring, and therefore Gandalf would presumably have been likewise capable.

However, what we can also take from that statement is that making a Ring is not a simple task; there is some "lore" involved, and we know from elsewhere that Saruman had made especial study of the Rings of Power, but yet Tolkien states that even he would have required knowledge found only in Mordor to complete his own work.

So, to summarise:

• Yes, but,
• It's neither quick nor easy, because,
• There is considerable "lore" involved, and,
• It requires hundreds or even thousands of years of dedicated study to get to a "Saruman-level" of "lore", and,
• Even then there will be missing knowledge which may only be found in Mordor.
• So for all practical purposes it's actually "No".