> Did you try \item[myref] and \in[myref]?
> 

This will do the job indeed.

\starttext
\startitemize[n]
\item One
\item[refTwo] Two
\startitemize[a]
\item A
\item[refB] B Test
\stopitemize
\stopitemize

see (\in[refTwo].\in[refB]) for Test



Is there some construction to combine an item reference with its parent item?

\startitemize[n]
\item One
\item Two
\startitemize[a]
\item A
\item[refB] B Test
\stopitemize

see (\in[parent, refB].\in[refB]) for Test