expression
A formal written expression used to embed a yes/no question inside a sentence. Often follows a plain-form clause. In spoken Japanese, ～かどうか is more common.
その情報が正しいか否かはまだ分からない。
We still don't know whether or not that information is correct.
参加するか否かを早めにお知らせください。
Please let us know whether or not you will attend as soon as possible.
Combination of the question particle か, the classical negative 否 (いな, 'no'), and another か. The pattern is a fixed formal expression.