\def\ShowSubscript[#1]{\switchtobodyfont[#1]#1: “₂”\par}

\starttext
\ShowSubscript[dejavu]
\ShowSubscript[antykwa-torunska]
\ShowSubscript[antykwa-poltawskiego]
\ShowSubscript[iwona]
\ShowSubscript[cambria]
\ShowSubscript[libertine]
\stoptext
