The equivalent of an AK-47 for sniper rifles doesn’t exist. The question itself cannot be properly answered due to the way it is worded. Since the AK-47 is not a sniper rifle, there is no equivalent. Some others have tried to answer your question by showing you other weapons that are (apparently) sniper rifles, they are not an equivalent to and AK-47 sniper rifle since the AK-47 is not a sniper rifle.
The AK-47 is known for its ability to function reliably under adverse conditions with little maintenance. Due to the way it is manufactured, parts are (for the most part) interchangeable between weapons. That is, parts from one AK-47 can be used in another. However, with an effective range of only 380 yards (350 meters), an AK-47 can hardly be considered a sniper rifle or used as one.
The effective range of a typical purpose-built sniper rifle will be in the 800 to 1000 meter range (875 to 1094 yards). Obviously, there is no comparison between the modern sniper rifle and an AK-47 with the effective range of the modern sniper rifle being 3-times that of the AK-47. One of the advantages of the AK-47 is its ability to put a lot of bullets downrange while a properly equipped sniper would eliminate the person with the AK-47 with one bullet way before the AK-47 was in range or close enough to the target to hit it. The simple answer is there is no equivalent.
AK-47 vs. Dragunov SVD
But if the question refers to a sniper rifle which has status as the AK-47 in the world of assault rifles, then the answer should be an SVD Dragunov. In fact, there is no “best” AK-47 or sniper rifle. But, same as the AK, SVD Dragunov is known for being an incredibly reliable platform in almost any condition you put it in. It’s hard to go wrong with any sort of Kalashnikov type rifle. As for sniper rifles, it depends on what you want to do with it.
The SVD Dragunov is a cheap and durable rifle widely used around the world in various conflicts and it also has a cult status as it’s counterpart among assault rifles (AK-47).