i just login into google adsense and created ads. Can i use this google advertisement code for all my blog. or do i need to create another advertisement code for my other blogs
Sure you can. However, you will not be able to track each site individually. So it's really not done.
you only need one adsense account for all your sites/blogs and use one code on all sites. however, if you want to track how each site is performing, you can either setup URL channels or assign channels to each ad code you generate so that you know which site or which ad is performing better.
yes, you can. So far as domain earning monitoring concern, you can setup URL channels in google adsense using Adsense Setup -> Channel Settings -> URL Channel Settings. For each domain, you create one url channel. After few hours, its impressions and earnings will starting showing in your adsense reports.
yes you can. and if it`s on blogspot than there is automatic way to do it within the monetize options
Sure you can but I would like to advice to you use channel. It can help you learn more about each adsense in different sites. Good luck.