There is no single such-that symbol. In set-builder notation the vertical bar \mid or a colon is read as "such that". In optimisation problems people write s.t., and older texts use ∋. Pick one and use it throughout a document.
All ways to write it
\midthe bar in set-builder notation, with relation spacingNo package needed:a colon, the other common such-that signNo package needed\coloncolon with punctuation spacing, as in f\colon A \to BNo package needed\ni∋, an older such-that sign, now mostly "contains as element"No package needed\text{ s.t. }the written abbreviation, common in optimisationPackage: amsmath\middle|a bar that grows with \left and \rightNo package needed
Commands marked with a package need that \usepackage line in a LaTeX document.
Example
\{ n \in \mathbb{Z} \mid n = 2k \text{ for some } k \in \mathbb{Z} \}The even integers: every integer n such that n is twice another integer.
Questions
Why use \mid instead of |?
Both print a bar, but \mid is a relation and gets space on both sides, which is what set-builder notation needs. A plain | is meant for absolute value and sits tight against its neighbours.
How do I write s.t. in an equation?
Wrap it in \text so it prints upright with normal spacing: \min f(x) ;\text{s.t.}; g(x) \leq 0. \text comes from amsmath and is built into KaTeX.
Is ∋ the such-that symbol?
Some older books use it that way, but today \ni (∋) usually means "contains as an element", the mirror of \in. Most readers expect a bar or a colon.
Using such that in Confluence
Confluence Cloud has no built-in LaTeX. With LaTeX Math for Confluence you add a math macro to any page, type \mid and it renders inline or as a block, with a live preview while you edit. Every command on this page renders there without extra packages.