If you mean the Loch Ness Monster or Nessie...you eventually locate it on your second trip to Loch Ness.
1) Travel to Loch Ness and get the digital camera by helping the man whose truck is stuck under the bridge (click tire, then the valve). Go right to the Pub and play darts to get a rowboat ticket. Take a photo of humps in the water, and eventually return them to the Mews lab. They are just tires, but a shadowy Nessie is also seen.
2) On your return to Loch Ness, complain to the rowboat operator, who leaves. At the Pub, play darts to earn a Submarine ride, and photograph the "Nessie" at the bottom of the Loch. Return to the Pub to find it is a movie prop, but after beating the first player again, you get a Pennywhistle from the bartender. Take the rowboat out alone and you can use the pennywhistle to lure Nessie for a picture. This closeup photo goes back to Mews and confirms the existence of the Loch Ness monster.
In the monastery.
There does not seem to be a horn on Cryptids Island. There is a flute (a pennywhistle) which you receive after the submarine ride, after you defeat the sore loser at darts again.
You find it caught on the fence of the farmer's brother.
Yes, you can find proof of The Jersey Devil, Bigfoot, Nessie, and the Chupacabra. (see related question)
There are some matches in the pub at Loch Ness.
Find all 4 cryptids
after you cut it it automatically goes into your inventory.
Dive to the bottom and then go left.
first you have to find all the other cryptids then you go in the helicoptor to the new location and follow him to his cave
The prize for spotting Nessie during the Cryptids Island preview (beginning December 2, 2010) was a Nessie Hat. (see related link)
You find him in the lab, where you first talked to him. From the helipad. it is just to the left.
If you use the sub, I think you will find/see? Nessie.