Calling this script in Nuke opens all file paths in the Explorer/Finder within the current selection of enabled nodes. It can also recurse into enabled groups and apply a filter that only opens paths from specific types of nodes, e.g. Read or Write.

open_file_folders.py

import os
import platform
import subprocess

def open_file_folders(nodes, filter = None, recurseGroups = True):
    for n in nodes:
        if n.knob('disable') and n['disable'].value() == True:
            #print 'skipping {0} because it is disabled'.format(n['name'].value())
            continue
        if recurseGroups and isinstance(n, nuke.Group):
            #print 'recursing into {0}'.format(n['name'].value())
            open_file_folders(n.nodes(), filter, recurseGroups)
        if filter != None and n.Class() != filter:
            #print 'skipping {0} because it is not of type {1}'.format(n['name'].value(), filter)
            continue
        if n.knob('file'):
            path = n['file'].evaluate()
            if path != None and path != '':
                print '{0}: {1}'.format(n['name'].value(), path)
                folder = os.path.dirname(os.path.abspath(path))
                if os.path.exists(folder):
                    if platform.system() == 'Windows':
                        subprocess.Popen('explorer "{0}"'.format(folder))
                    elif platform.system() == 'Darwin':
                        subprocess.Popen(["open", path])
                    elif platform.system() == 'Linux':
                        subprocess.Popen(["xdg-open", path])

open_file_folders(nuke.selectedNodes(), 'Write')