You are referring to the ditto mark, which is actually a special Unicode character (U+3003) looking like this:
Unicode Character 'DITTO MARK' (U+3003): 〃
Using XeLaTeX or LuaLaTeX, you could use this character directly, provided that you use a font the has support for this symbol. However, the Wikipedia article cited above mentions that
[...] in practice closing double quotation marks (”) or straight double quotation marks (") are often used instead [of the Unicode symbol]
so you might as well use something like
\newcommand*{\dittoclosing}{---''---}
\newcommand*{\dittostraight}{---\textquotedbl---} % available in T1 encoding
(The latter requires you to use \usepackage[T1]{fontenc}
).
The result looks like this:
