Someone else already asked here
How do you read these kanji 年々?
(I am just making sure that I understood.)
In the following sentence, 年々 is read【ねんねん】, correct?
小学校入学【しょうがっこうにゅうがく】を控【ひか】える子【こ】どもたちのランドセル選【えら】びが、年々【ねんねん】過熱【かねつ】しています
The selection of school bags for children about to enter elementary school is becoming more and more heated every year.
https://www.asahi.com/articles/ASQ6S62NTQ69DIFI00D.html?iref=comtop_Opinion_01
Yes, it is ねんねん.
As an additional comment, ねんねん is the more common in the first place. And you can most probably always read 年々 as ねんねん if it is not followed by particles.
A example of 年々{としどし} is like:
which could be 収入は年年{としどし}変わる with some elements dropped.
Generally ねんねん is used when referring to monotone change (usually increase/decrease) whereas としどし is for fluctuations. Possibly comparable to English year by year vs from year to year.
