Scopus and Web of Science give different h-index: who should I trust?
Both (and neither).

Like other citation metrics, the h-index compiled by these databases only depend on what's already in those databases. Both of them have quality barriers, which means you could well have been cited somewhere else but neither of these indexed it. That's why your Web of Science h-index is almost certainly going to be lower than your Google Scholar h-index. In the same way I'd guess that your Web of Science h-index is lower than your Scopus one.

In other words, your h-index depends on what database is used to generate it. You could say your h-index is 15 and it wouldn't carry meaning; you need to say your h-index is 15 as measured by Web of Science.

I'm not sure how seriously the job you describe treats the h-index. If given the option, I'd report both of them (and the one by Google Scholar). Otherwise just give the higher number, and expect to defend it in the interview.