Which question in MO has had maximal total bounties among other questions? I mean the total bounties which are given by the asker or other participants.

6$\begingroup$ I think this question is a good candidate  the OP offered one ounce of fine gold for a correct answer.  Of course this depends on the exchange rate between gold and MO points :) $\endgroup$ – Stefan Kohl Jun 19 '15 at 19:08

1$\begingroup$ @StefanKohl, can any amount of fine gold ever be worth more than an MO point? :) $\endgroup$ – Joonas Ilmavirta Jun 19 '15 at 19:11

$\begingroup$ @JoonasIlmavirta thank you for your revision of this question and also your answer to it. $\endgroup$ – Ali Taghavi Jun 19 '15 at 19:39

$\begingroup$ @AliTaghavi, you are welcome. I'm glad if I could be of help. And I won't be offended if you want to undo or overwrite my edits. $\endgroup$ – Joonas Ilmavirta Jun 19 '15 at 19:59

$\begingroup$ @JoonasIlmavirta thanks for your kind message. of course your revision was very necessary, and your answer was very helpful. $\endgroup$ – Ali Taghavi Jun 19 '15 at 20:19

1$\begingroup$ @JoonasIlmavirta If you are willing to trade ounces of gold for MO points, we may be able to come to an arrangement. :) $\endgroup$ – David E Speyer Jun 30 '15 at 13:51
The Data Explorer is the perfect tool for this kind of questions. The highest possible single bounty is 500 points. (For details of bounties, see this and this help page.) See the query Questions that received a lot of bounty. It gives a list of questions that have received more than one bounty, sorted by total amount. These exceed 500 points:
 When does a modular form satisfy a differential equation with rational coefficients?, 1000 points (2 bounties)
 The error in Petrovski and Landis' proof of the 16th Hilbert problem, 700 points (3 bounties)
 Distributivity of group topologies on $\mathbb Z$, 600 points (2 bounties)
 Godel on recursiontheoretic hierarchies, 550 points (2 bounties)