Find swapped nodes in BST
computeSwappedNodes (root, new PrevNode(null), list);


Unneeded space between function name and parentheses with arguments. You do this multiple times.

/**
 * Returns the 2 nodes which if swapped results in binary search tree.
 */
public int[] getSwappedNode( ) {


No, you return the items stored within. Not the nodes. You don't fulfill the assignment as stated. Additionally, you return multiple nodes, so name the method getSwappedNodes. Lastly, no need for a space in an empty set of parentheses.