HOW CAN I TELL IF ITS REAL OR FAKE
KK - There is a VTRAQUE VNUM 0M 1745. But whether or not yours is fake, is kinda hard to tell without personally looking at it.
The coin looks like a sea salvage piece. It appears to be an 1745 Pillar Dollar (8 reales) struck at the Mexico City Mint under Spanish rule (M° mint mark, MF -assayer). Pillar Dollars were minted all over South America from 1733 to the end of the 18th century when they were replaced by 8 reales featuring the portrait of the current Spanish King (These were known in the Americas as "Portrait Dollars".
Generally, condition is an important component of value. Some sea salvage pieces transcend this requirement if they can be attributed to a specific important shipwreck. For example, coins from the Atocha (1622) are worth far more than similar unattributed pieces because of their association with this famous shipwreck. Without the attribution the coin has to stand on its merits. Pillar dollars in damaged condition, similar to this piece, bring about $10 or so in the numismatic market place. 1745 is not a particularly rare date for a Mexico City piece. Coins grading EF (Extremely Fine - non-sea salvage are worth about $125).
Here's what one looks like.
how can i tell if it is from atocha?
The easiest way to do that is to take it to a professional coin collector (numismatic expert) who is also somebody who sells them. He will view the coin using his loupe.
The coin should weigh as much as 27 grams. The coin should have floral edges and not milled edge.