You have a manually altered novelty item, known as a Magician's Coin, made by altering two normal coins and gluing the pieces back together, that sells regularly for a couple dollars. Use a magnifier and examine just inside the raised rim on both sides of the coin, looking for a seam where the pieces are joined, that can be on either side of the coin.
Double headed novelty and Magician's coins have no numismatic value, but depending on the denomination an quality most are under $10.00.
In some cases, a double die adds to the value of a coin but in other cases it does not. Whether or not the value increases by the presence of a double die is determined simply by the market demand for them. For this Kennedy half I find the value in uncirculated condition to be about $18.
It depends very much on the coin's date. Please check the questions "What is the value of a <date> Kennedy half dollar?". E.g. if your coin is from 1969, look for "What is the value of a 1969 Kennedy half dollar?".
Half a dollar
What is the value of this half dollar
Either not Kennedy or not a dollar. Please look at the denomination on the back.
Sorry it only has face value.
A Mint State 1971 Kennedy has a retail value of $1.00-$2.00
Check that coin again. Kennedy wasn't put on the half dollar until 1964.
the 1972 Kennedy half dollar is worth 50 cents in circulated condition, or about a dollar in uncirculated condition