Is there an index or ETF which follows this pension fund's investments?

No. The up-to-date composition of the fund is not public nor should it be due to the very real possibility of moving the markets in unintended ways. However, they do publish annual reports of investments which you can access on their website. Here's a 2015 one: https://www.nbim.no/contentassets/70de238e3f6747228b76a99ec2...