What are the good service intervals for the DNM USD-6 fork? How to understand that it should be maintained first? What are the recommended procedures for this?
The manual linked in the comments states that the fork should be serviced every 10 months, every year or every two years, depending on its usage conditions, at an authorized shop.
The service intervals are expressed in terms of months of owning rather than in riding hours. However, the suggested maintenance intervals lie in the expected order of magnitude for values for how often people service their forks in the real world (from twice a year to once in two years, depending on the usage).