It's used in differents domains

See TREC QA Collection - http://trec.nist.gov/data/qa.html

Related (but not restricted) to the Linked Data domain, QALD provides a benchmark for multilingual question answering, as well as a yearly evaluation campaign.

http://greententacle.techfak.uni-bielefeld.de/~cunger/qald/

The StackExchange's dataset is a very rich one: https://archive.org/details/stackexchange

This is composed by all the public data from all platform's sites.

https://archive.org/details/stackexchange

Actually QALD also provides hybrid questions as well as questions from the biomedical domain. In the BioASQ project (http://bioasq.org) we also created benchmarks (domain: bio-medicine) with more than 800 questions. 

I registered as a participant in bioasq.org.. How can i download the benchmark dataset

SQuAD and 30M Factoid questions are the recent ones. If you are looking for a limited set of benchmark questions, I suggest you to look at https://sites.google.com/site/ontomcqs/research , where we have made a few benchmark sets for question authoring application.

The SQuAD is one of the popular datasets in QA which is consist of some passages. Each question can be answered by finding the span of the text in the passage. So it is useful when you are building a QA model based on information retrieval (IR) and Reading Comprehension (RC):

https://rajpurkar.github.io/SQuAD-explorer/

HotpotQA is also a QA dataset and it is useful for multi-hop question answering when you need reasoning over paragraphs to find the right answer.

https://hotpotqa.github.io/

The other datasets:

https://stanfordnlp.github.io/coqa/

https://research.fb.com/downloads/babi/

https://github.com/brmson/dataset-factoid-webquestions

https://wiki.dbpedia.org/datasets

We published a list of large QA datasets at https://github.com/ad-freiburg/large-qa-datasets including links to the corresponding publication and dataset.