Which web technology to learn for an experienced C++ developer?
Hit's per day isn't a really useful metric for estimating performance. You really need to be concerned with the peak load and the acceptable response time.
80-100k hits per day is an average of about 1 hit per second. The hits are not going to be evenly spread out, so for normal traffic you might expect a peak load of 10 hits per second.
If you are going to promote the site with newsletters or commercials, expect to peack at 100's of hits per second.
If you selling $1 air tickets, expect to peak at 1000's of hits per second.
Now the language you choose for the site isn't nearly as important as your choice of database (not necessarily relational) and the way you store the data in the database.
Scaling up frontends is relatively easy, so having really fast efficient HTML generation shouldn't be a primary concern. Pick a platform that is going to be efficient for development time.
Friends, 
I've got some exp in c++ and now kind of starting my way to J2EE (to survive:))). Meanwhile, I've got a plan to venture in to a web portal my own. But with very little experience in web technology, I'd need to start from scratch. I'm little confused on which way to go and I'm here. 
PHP, Python or JSP, considering the fact that, anyway I've got to learn J2EE at my work.
Would that be worth to learn PHP or Python to develop a portal which I expect to get 80-100K 
hits per day "IF" everything goes well OR jsp would be sufficient? 
Many thanks