Citation of an article is not reflected in Google Scholar database Some of my published articles have been cited by an article published in March 2017. But surprisingly citation to my articles is are not being shown in Google Scholar. What could be the reason? Where should I place my query for citation update?
In addition to "indexing takes time (if it is done)" and taking into account that your journals in view are SCI indexed, consider Clarivate Analytics' / Thomson Reuters' Web of Science as a subscription based alternative bibliographic database. It has historical roots to the SCI (source).

Perhaps field dependent, but from own recent experience in chemistry, between appearance on the publisher's site (Wiley) of an about 1 year-old journal and Web of Science the gap was just about half a year.  To accelerate visibility of your work during this period, you may import publications as yours via the doi in the ORCID database, and simply link to the your personalized profile page there.

It is equally possible that your publication's abstract appeared on other sites than the one of the publisher's and consequently was cited.  Scopus (more oriented towards engineering than sciences, backed by Elsevier) is a potential source.  ResearchGate and the listings of Mendeley' catalogue add to it, too.