I was wondering is there a limit to the amount of reputation points one question can receive and if not, what the highest you have ever seen or heard of?
No, there is a daily reputation cap on the amount of reputation you can earn per day, but there is no limit on the amount of reputation you can receive per post (question or answer).
This would be really difficult to quantify because votes =/= rep. There's no limit to votes or reputation on a question (in general) but there is a daily rep limit of 200 points on a per site basis...
So... on a question, if someone gets 40 upvotes in a day at 5 points per vote (assuming that's their only post getting votes on that site - which is a very unlikely event), they've hit their rep cap for the day and any additional upvotes will not earn them any rep... but they still get the votes.
Similarly with answers, 20 upvotes in a day at 10 points per vote gets to the rep cap and that's it for that day.
So, when you look at historical questions with huge numbers of upvotes, how much rep that question actually earned a person varies depending on whether they hit the rep cap on different days and how many votes were posted between hitting the rep cap and midnight UTC.
So, as an example:
Someone who only has one question earning votes gets 30 votes every day for 10 days. At the end of 10 days they earn 30*5*10=1500 rep for 300 votes.
Someone else who only has one question but it gets a lot of initial attention earns 60 votes per day but the question peters out after 5 days. After those five days, they have the same number of votes (60*5=300) but, due to the rep cap, they only have 200*5=1000 rep.
So, the first person has 500 more rep because their question wasn't quite as popular!
To be slightly pedantic, there is a practical maximum on the amount of reputation a question can earn its asker based on the age of the question.
The absolute maximum reputation a question can earn for an asker in one day is 200 1 due to the daily reputation cap. This can only happen if it is the only content of the asker's that gets upvoted that day.
So the maximum reputation one can get from a single question is (the age of the question, in days) × 200.
The oldest (and largest) site in the network is Stack Overflow. The oldest question on that site is from July 31, 2008. If one of the questions from that day received enough upvotes to reach the daily reputation cap every day (and the asker didn't gain reputation elsewise) the asker will have earned 544,400 reputation points ((2,722 days between 2008-07-31 and 2016-01-13) × 200).
1 Discounting the +2 bump the asker would receive for accepting an answer to the question.