Contract Bridge: Revoke first noted by dummy
Citations in this answer are to the 2017 Laws of Duplicate Bridge).The Laws  of Rubber Bridge are very similar.
Relevant Laws
LAW 9 (PROCEDURE FOLLOWING AN IRREGULARITY) A 4 (page 13) says:

Dummy may not call attention to an irregularity until play of the hand is concluded
(This corresponds to law 13 for Rubber Bridge)

Under Law 43 (Dummy's limitations) (page 49 of the law booklet), Law 43 A (1)(b) and 1(c) says:

(b) Dummy may not call attention to an irregularity during play.
(c) Dummy must not participate in the play, nor may he communicate anything about the
play to declarer.

Law 43 A 2 and A 3 say:

2.(a) Dummy may not exchange hands with declarer.
(b) Dummy may not leave his seat to watch declarer’s play of the hand.
(c) Dummy may not look at the face of a card in either defender’s hand.

A defender may not show dummy his hand


Law 43 B 3 says:


If dummy after his violation of the limitations listed in A2 is the first to draw attention to a offender's irregularity, there is no immediate rectification. Play continues as though no irregularity had occurred. At the end of play
if the defending side has gained through its irregularity the Director adjusts only its score, taking away that advantage. The declaring side retains the score achieved at the table.


(This corresponds to law 43 for Rubber Bridge)
Law 63 A (page 70) msays
(This corresponds to law 43 for Rubber Bridge)

A revoke becomes established:

when the offender or his partner leads or plays to the following trick (any such play, legal or illegal, establishes the revoke).
when the offender or his partner names or otherwise designates a card to be played to the following trick.
when a member of the offending side makes a claim or concession of tricks orally or by facing his hand or in any other way.
when agreement is established (as per Law 69A) to an opponent’s claim or concession;


Law 64 (PROCEDURE AFTER ESTABLISHMENT OF A REVOKE) C (1) (page 72) says:

When, after any established revoke, including those not subject to trick adjustment, the Director deems that the non-o‘ending side is insufficiently compensated by this Law for the damage caused, he shall assign an adjusted score.

(This corresponds to law 64 for Rubber Bridge)
Analysis
It is not explicitly said in the question that the revoke was established. If it was not it should have been corrected and play should have proceeded.
If the revoke was established and dummy called attention to it during play, there should not have been an automatic two-trick adjustment, Instead, play should have continued. After play was complete, the damage done by the revoke, if any, should have been assessed, by the Director in a duplicate game, by the Arbiter in a club rubber game or any game that has an Arbiter, or by the players in any Rubber game without an Arbiter. The damage done by the revoke should have been restored. That is, if the revoke led to the offenders taking one trick more than they otherwise would have, the non-offenders would be awarded a one-trick adjustment, or whatever number of tricks difference the revoke caused. If there is honest doubt as to hoe much damage was done, it should be resolved against the offenders.In a duplicate game under Law 43 B 3 there would probably be different scored assigned to the two sides by the Director.
If the dummy called attention to the revoke after play was complete, the normal two trick adjustment should have been made. However, if the damage was more than two tricks, the adjustment should restore all damage, to result in the same score that would have been achieved if the revoke had not occurred.
In no case should the had be thrown in because of a revoke, or because of dummy calling attention to a revoke.
In a duplicate game the Director would, if there was doubt, and if feasible, conduct a poll of players of similar skill level to help determine the amount of damage.
In an informal friendly game, dummy might kibitz (watch) declarer's play, although this would violate law 43 A 2 in a duplicate or club rubber game. But even in a friendly game it is a bad idea fro dummy to be looking at the cards still in the hand of either defender, and if dummy does watch declarer, s/he should be particularly careful not to make any comment on the play, or call attention to any error or irregularity until play is complete.
Without the hands and the play up to the point of the revoke, I cannot independently asses the damage done by the revoke.
Background
I am a qualified ACBL club director who ran a small bridge club for a number of years, prior to 2010.