I wanna know how to extract the last modification date of a DBpedia page (for example: http://dbpedia.org/page/Cristiano_Ronaldo)?
There is no last modification date of a DBpedia page.
The extracted data is based on the Ronaldo Wikipedia Page. You can detect the Wikipedia Page version, due the date of the wiki page version, too.
The predicate you need to get that information is:
It has the following value:
Then you can go to the English Wikipedia and search for Christiano r. and click on view history on the top right. Afterwards you click on a date of one revision (doesn’t matter which one). Then you accessed a URI of the form
Next, you replace the number after oldid= with the value of the wikiPageRevisionID.
On that Wikipedia Page, you see the date of the revision.