Nearest point

There is no algorithm I know of to work off the array. There are two options that I see (assuming your indeed has TopoDS_Vertex objects):

1-Iterate through the array and keep the one with the minimum distance. So, if you have a gp_Pnt (myPoint), you can call
myPoint.Distance(BRep_Tool::Pnt(myTable(i))) to get the distance. Note that it is even more efficient to use SquareDistance instead of Distance.

2-You can also put all the vertices in a compound. Then, you simply need to use BRepExtrema_DistShapeShape to get the nearest. Note, however, that this will only give you the nearest vertex, not the index into your array (if that is important).