The standard reference for the series is Attribution Guide of United States Large Cents 1840 - 1857 by J R Grellman and Jules Reiver. This isn't a book you will just be able to go to the library or a book store and just pick up. If you are lucky you might be able to get it through inter-library loan, or if you are an
ANA member from their library. You might be able to get it from a numismatic literature dealer, and it is available from the author Bob Grellman, but it is a $100 book.
If you just want to check to see if this piece may be a proof check these things on the reverse. Look for a rust lump on the top surface of the N in UNITED where the diagonal meets the right upright. Another rust lump on the top surface of the R in AMERICA in the middle of the right leg. Look for the appearance of the Ein ONE being punched over another letter. The evidence will be in the field area between the middle serif and the bottom leg of the E below it. If you find those things you have N-3. (Proof only)
If they aren't there, look for fine die polish lines covering the entire reverse of the coin running down to the right. Look for a die spike running down to the left in and from the denticals above the TE in STATES. Look for a strong lump on the bottom edge of the right foot of the T in CENT. If you see these things then you have N-5 (proof only)
If it doesn't match these look for three strong lines down from the earlob. N-4
Several fine die lines from the denticals to UNIT. N-2
There are other identifying features but those are the strongest ones.
Sorry I don't have pictures of the diagrams from the book available. I wouldn't post them anyway because of copyright restrictions.