Here is the output of mtxrun. Note that there are two versions: T (title) and ST (subtitle). I want the title version.
mtxrun --script fonts --list --all --pattern=DTL
identifier familyname fontname filename subfont instances
dtldocumentaitalic dtldocumenta dtldocumentasansstitalic DTL Documenta Sans ST Italic.otf
dtldocumentanormal dtldocumenta dtldocumentasansstitalic DTL Documenta Sans ST Italic.otf
dtldocumentaregular dtldocumenta dtldocumentasansst DTL Documenta Sans ST Regular.otf
dtldocumentasansst dtldocumenta dtldocumentasansst DTL Documenta Sans ST Regular.otf
dtldocumentasansstitalic dtldocumenta dtldocumentasansstitalic DTL Documenta Sans ST Italic.otf
dtldocumentasansstregular dtldocumenta dtldocumentasansst DTL Documenta Sans ST Regular.otf
dtldocumentasanst dtldocumenta dtldocumentasanst DTL Documenta Sans T Regular.otf
dtldocumentasanstcaps dtldocumenta dtldocumentasanstcaps DTL Documenta Sans T Caps Regular.otf
dtldocumentasanstcapsregular dtldocumenta dtldocumentasanstcaps DTL Documenta Sans T Caps Regular.otf
dtldocumentasansteuro dtldocumenta dtldocumentasansteuro DTL Documenta Sans T Euro.otf
dtldocumentasanstitalic dtldocumenta dtldocumentasanstitalic DTL Documenta Sans T Italic.otf
dtldocumentasanstregular dtldocumenta dtldocumentasanst DTL Documenta Sans T Regular.otf
I tried \definefontfamily[DTL-Documenta-Sans-T][ss][DTL-Documenta-Sans-T] but it does not work with \sc.