I have a jar full of Jefferson Nickels from 1930's-1980's What would be the error coins or dates I should look for? can anyone help?
I suggest you buy A Guide Book of United States Coins also know as the Red Book. There's plenty on eBay and you will just need a recent one; it's not necessary to get the newest, at least for a start.
1938 D and S as well as 1939 D and S and 1950-D are the major dates to keep an eye out for. Also, any "war nickels" produced from 2942-1945. These contain 35% silver and so are worth a little bit more there. They are easily recognizable because the mint mark was moved to above Monticello on the reverse and is very large.