The citation information is given on the right navigation bar next to each article:
If you use a bibliographic citation manager such as Endnote, use the links underneath the citation information to export the citation.
Alternatively, you can copy & paste the citation information into your clipboard by clicking on the blue button "Copy Citation to Clipboard" (use command-V on a Mac or CTRL-v on Windows to paste the citation into your application).
As JMIR articles are electronic only, the do not have page number, but instead an article-ID (e.g. "e108"). This is a common way to cite electronic articles. Do not omit the article-ID from your citation. Use it instead of page numbers.