import os, nuke

inputPath = nuke.getFilename("input")
inputDir = os.path.dirname(inputPath)

projFolder = os.path.basename(inputDir)

for n in nuke.allNodes():
    if n.Class() == "Read" or n.Class() == "ReadGeo":
        
        oldPath = nuke.filename(n)
        if not os.path.exists(oldPath):
        
            pathTuple = oldPath.partition(projFolder)
        
            fileKnob = n.knob("file")
            fileKnob.setValue(inputDir + pathTuple[2])