After awarding PhD, if the PhD work is not worth or scientific misconduct of experiments etc. whether Can it be challenged? I found people getting PhD without studying the concerned subjects for the work and did not do the experiment. Pictures and results were manipulated. published in Journal and got the Ph.D (by publishing in Paid journals and bribed the external examiners)

During this case, can we challenge the PhD degree? Kindly let me know what is the procedure.
Depends highly on the university.  In the US, this would be a case to take to the dean of the graduate college, or an office of research integrity, if one exists and the problem is more systemic within a lab or group.  My university has an office that handles all allegations of research misconduct &amp; ethics, for instance, but for issues regarding students, this is typically handled by a dean.  As Buffy says, getting a PhD revoked is probably going to be very hard, but this seems like a more systemic problem that should be brought to the attention of the school.

For the most part, US universities (perhaps with the exception of "for profit" schools) take this sort of thing very seriously.  In other parts of the world, the incentive structure is usually somewhat different and the university may not take steps to rectify the situation.

I suppose the other question you have to ask yourself is this: does this just make the students look bad, or the whole university?  It sounds like you may be a PhD student at the same university, in which case you would prefer if the university maintains a good academic integrity reputation, and hence pursing this at the institutional level might be worth it.  If you think it's just a few "bad apples", then it might not be worth your time - their misconduct won't win them any favors and will probably sort itself out.