Here's why:
* "Is this are you looking for" is a mix of two different sentence structures.
* "Is this..." starts a question about an object.
* "...are you looking for" is a phrase that would be used to complete the sentence.
Here are some ways to correct the sentence:
* "Is this what you are looking for?" This is the most natural and grammatically correct way to phrase the question.
* "Is this it?" This is a simpler way to ask the question, if the context is clear.
The choice depends on the situation and the level of formality you want to convey.