In 3D space, an infinite number of vectors may be perpendicular to one vector. You need to be more specific.
If you have 2 vectors, you can calculate the cross product to get a vector perpendicular to both of them. In this case, only 2 results are possible.
If you only have one vector, you can rotate it 90 degrees to have a perpendicular vector. But then again, you’ll need a second vector to be the rotation axis.