I think it is the suffix -i. Also if it was indefinite, newspapers should be singular 'gazete' not plural 'gazeteler'
you read newspapers = sen gazete okursun
you read the newspapers = sen o gazeteleri okursun / sen gazeteleri okursun
you read the newpaper = sen gazeteyi okursun / sen o gazeteyi okursun
it is -i :D
OK, so here we have a plural specific direct object gazeteleri. And the accusative suffix follows the plural suffix. So which vowel does the accusative suffix harmonise with? The e/a of the plural suffix? Or the last vowel of the root word (which is also e here, but it might not be).
It always goes with the last vowel is whatever it is attaching to, in this case "gazeteler" :) Another example would be "köprüleri" (meaning "the bridges" as a direct object)
Thanks! A helpful answer despite the typo in my original comment (now edited).
So its only correct to add "i" to a plural noun if its an object not subject?
Well, yes and no. If you have that as the subject, it would give the meaning of "his/her/its X"
When a direct object, it makes whatever you are talking about specific. :)