It would be Call of Duty: Black Ops 4. The Promotion site at ASUS doesn't seem to work at the moment though. -> https://promotion.asus.com/en...

Translation of the promotional description of the german page of Digitec:

When you buy a selected Asus product, you get Call of Duty: Black Ops 4 for free.

Procedure:
1) You buy a selected product of your choice
2) You will receive a claim code from us by e-mail.
3) Visits https://promotion.asus.com/en...
4) Create an account or log in
5) Redeem the claim code, upload the receipt.
6) Get the game code for Battlenet

In order for you to redeem this bonus, we will send you a code on the following dates.
- Ordered until and including October 11th: E-mail delivery on October 12th.
- Ordered until and including October 18th: E-mail delivery on October 19th.
- Ordered until and including November 8th: E-mail delivery on November 9th.
- Ordered until and including 29 November: E-Mail dispatch on 30 November.
- Ordered until and including December 30th: Email will be sent on December 31st.

You can then redeem the code on the ASUS website. You register and upload your proof of purchase. You will then receive the game code, which you can redeem directly on Battlenet. You must be of age to play the game. The age verification takes place on Battlenet. You can get a maximum of one code per customer, so if you buy a graphics card and a monitor, you still get only one code.

Valid from 10.09.2018
Valid until 31.12.2018
Deadline 31.01.2019