Where can I learn about celtic knot knitting and take a class?
In the US or Ireland?
Most yarn shops offer classes. Find one in your area and call them or visit their website. The web site, www.plantetpurl.com, is useful for finding shops all the US and in Europe. I googled celtic knot knitting and it looks like a slightly complicated form of cable knitting. Even if the shop you find is not familiar with celtic knot knitting they may be able to help you figure it out from a well written pattern. Good luck and happy knitting.
If you can knit and purl, the rest is moving these stitches around. However some directions can be confusing or poorly written. As mentioned above, a knitting shop is invaluable.