Could it be permitted to attend a conference talk on a secular subject, during a yom tov or shabbos, which will be of immediate benefit to one after the Yom tov or Shabbos? I am assuming that if one did so, they would do so without transgressing other halachah (such as driving, muktzah, writing, etc).

Shalom, Firstly let me apologize for the delay in answering your question. We have had some technical problems at the site, and I only now received your question. In general, the observance of Shabbat precludes attending conferences and talks that are not connected to Torah and the Shabbat atmosphere. However, in special situations it could be that there is a need to attend such a conference. If the need is truly great then, after taking precautions against breaking the Shabbat, one could attend. This is a general answer - but ... As conferences of this nature are usually held in hotels, and as hotels become more and more electronic, it is not so simple to ensure that the Shabbat can be kept - even just using the toilet facilities in many hotels involves electric eye taps etc which are problematic on Shabbat. Certainly if the conference involves missing synagogue services or Shabbat meals the question is more difficult. Questions of carrying, microphones, being filmed etc also need to be addressed. So in every case, my advice is to turn to a Rabbi who can weigh up the situation and also guide you in how to avoid Shabbat infractions. Blessings