There are three basic ways that I know of to produce harmonics. They are produced when you momentarily divide the string into 1/2, 1/3, 1/4, etc… of its length when striking it.

The 12th fret divides the string in 1/2, the 7th into 1/3rds, 5th into 1/4ths. Just behind the 9th is 3/5ths and divides into fifths producing a major 3rd, and so on. The partials higher than that are very hard to produce.

Second method is done by fretting a note, and then placing a finger lightly 12 frets above that note and plucking the string with the thumb while lifting the damping sound. I don’t know if this can be done with a pick. Tommy Emmanuel uses this a lot. Check his arrangements of Over the Rainbow or Michelle. Not sure what the name is for this. It’s the same as the first way, except you are shortening the string by fretting it, and you have to do the plucking and damping with one hand.

Third method is pinch harmonics. Here you are picking halfway between where you are fretting and the bridge, and you allow the pick and the flesh of your fingers to hit the strings at almost the same time. The easiest way to do this, I found was with an upstroke where the fat flesh of my fingers brushed the string just as I was picking. I can also get it on a downstroke using the flesh of the side of my thumb just trailing the pick. This is a cliche in hair metal solos, but was used by Clapton on Bell Bottom Blues, by Robbie Robertson a lot, and a bunch of others (Roy Buchanan, Jerry Garcia, Jeff Beck etc..)

Oh, and almost forgot method four, where you simply slap the string at the point where harmonics would be produced. Quickly slap the strings at the 12th fret. Now bar at the 3rd fret and slap on the 15th. Preston Reed uses this in his two hand tapping/drumming pieces for acoustic guitar.

Search on Youtube for “how to do guitar squealies”. Some guys are very fast and accurate at it, and I can do them pretty good if I work at it for a while first.