A Journal is indexed in Scopus and Web of Science. But under Web of science it is under Emerging sources citation index and not under SCI or SCI expanded. What are the pros and cons of publishing in it if you are a serious researcher looking for phd admission? Its not predatory for sure and no charges for author whats so ever. Its also from a reputed publisher. The feild is applied mathematics
I'm guessing that where you are in your career it matters very little. The important thing is to get published in a reputable journal. I also doubt that experienced scholars worry very little about such things.
Pick a journal that seems appropriate for your work. Send it off. Then write the next paper.
And if you are not yet in a doctoral program, then publishing is a big win, no matter where, as long as the journal is reputable.
In general you publish in the most prestigious journal that will accept your work. There are reasons for this: more prestigious journals tend to be more visible (more readers), more impressive (helps with graduate admissions), or are even tracked by promotion committees ("to be promoted to [role], you need to publish [number] articles in SCI-indexed journals"). So your question is rather difficult to answer. There's practically no reason to publish in an ESCI journal instead of an SCI journal.
That said, you should of course discuss with your advisor which journal to submit your article to. SCI journals might be more prestigious, but if your work is not significant enough and they are going to desk reject it, you might as well save yourself the time and submit to an ESCI journal.
It is generally considered a journal that accepts research papers that are then sent by editor to two experts in your field to be peer reviewed and accepted or rejected by the editor. It is difficult to advise you with out further information: where is the institution you are associated with, your academic achievements and future plans. Normally you would have an academic advisor who had supervised your research.