All About Pocket Knives

Can you use a Harbor Freight 110 volt spot welder to weld a nickel silver bolster to a nickel silver liner scale or a nickel silver bolster to a cutlers brass liner scale. Or would it take a Harbor Freight .220 volt. Or can a spot welder only weld stainless

I can't answer your question but I ran a spot welder once to weld stamped steel parts for Honda. The 220 volt may put out a hotter weld if you have 220 available or more heat ranges.

Why not solder?

Solder would be the way to go when attaching bolsters. You don’t need a super strong weld because the pins actually hold/tighten the bolsters. Be careful though especially if you liners have handle material on them already because several may react adversely to the heat. Adhesive may be another option just to hold them in place until you can peen them.

That spot welder will not work.
The liner will get a hole blown in it, and the bolster will just get hot. You need similar/same size items to actually make a penetrated weld. Silver solder is the way to go. You can even solder dissimilar metals.
Stay Brite is the brand I use on Stainless, and aluminum. Harris is the manufacturer.

A MAP gas torch is all you need...

Seems to me that spotwelding this would be overkill. And what are you going to used as a test material to make sure the spot welder is going to do an adequate job? Bolsters on knives have been soldered for a hundred years or more and works, why reinvent the wheel? I have soldered many bolsters on knives and never had any issues. Some manufacturers used spotwelding because they are mass producing many thousands of units and once setup and tested will save time. But for just one or few units would not be time effective.