How do I create a possessive or genitive citation?

If you're submitting to a journal or conference proceedings, the publisher's template may have defined a custom command for creating genitive or possessive cites (e.g. Smith's (1990) study shows...), so check the template provided—and any instructions to authors.

Otherwise, you can create such cites depending on which package is used. Here are some examples:

Using harvard

\usepackage{harvard}
\possessivecite{Smith:1990}

Using natbib

\usepackage{natbib}
\citeauthor{Smith:1990}'s \citeyearpar{Smith:1990}

Using biblatex

\usepackage[backend=biber,style=authoryear]{biblatex}
\citeauthor{Smith:1990}'s (\citeyear{Smith:1990})