What knitting/weave style is this?
Is it doable by hand?
Yes, every knitting pattern is doable by hand. You might need some tutorials and experience to make it look good, but it's doable by hand. The main problem with such a light product is that it uses very light yarn, thereby needing a great number of stitches, increasing the time it takes to knit.

What is it?
To be honest, I'm not absolutely sure. There are several stitches that create a similar pattern. By looking at the transition from pattern to cuff you can count 4 stitches that form the repeating pattern.

The best match seems to be the seersucker pattern. This one is relatively easy to do because all the stitches you need to know are knit and purl. Here you can find a detailed picture of both sides of the pattern to compare it with your hat, as well as a written instruction. There are also instruction on Youtube.

A very similar look is produced by a mock honeycomb pattern. Have a look at a video tutorial here.

It could also be a bubble pattern, but with very small bubbles. The instructions here, as well as this video tutorial work with 4 stitches, just like in your hat.

Please note that all video tutorials demonstrate the english knitting style, where the yarn is "thrown" by the right hand. You can create the same pattern in continental knitting style, where the yarn is lead by the left hand.