JSitemap integrates third party web services to retrieve informations about your site through Google and Alexa.

It could be the case that your site has no every kind of stats informations available, in this case the report will show a 'N.A' notice. In this case you can visit the Alexa official site http://www.alexa.com/ and perform a search for your domain.
In the case that some informations or certifications are missing in order to be ranked, you can correct this issue being the owner of the domain and providing required data to Alexa.

Also the Google page rank could not be assigned and thus not retrieved in the SEO stats, at the time of writing Google stated that new sites could even not get a page rank assigned based on the Google latest specifications, or at least it could require several months.