We are in Vienna and would like to watch a sitting of the Austrian Parliament. Naturally we would prefer to visit at a time when there are likely to be lively debates in a fully attended house, with speeches by the leaders of the government and opposition parties. In the British Parliament, this tends to happen in the House of Commons's Prime Minister's Questions (PMQ), which is scheduled for every Wednesday at noon when Parliament is in session. Does the Austrian Parliament have anything similar? I know that the agendas for both houses are posted on the Parliament's website, though it's not clear to me whether there are any regularly scheduled debates akin to PMQ.
As you can see in the agendas, you are probably out of luck. Additionally, I think that most of the sittings listed named like "X-Ausschuss" are only partially public and you may need journalist accreditation to attend (especially the BVT-Untersuchungsausschuss).
More information can be found on the English website but I guess you have already seen that. I would suggest you ask the visitor service directly using the phone number provided on that site.
If you are still in Vienna, check if you can go visit the emergency session scheduled for
tomorrow Monday, 19.05.[several parties wanted a session immediately as of Saturday] this week[later date was pushed back] after EU elections - it is sure to be dramatic and lively as the resignation of the vice chancellor and the associated scandal are to be dicussed.