jrf on "[Plugin: WordPress SEO by Yoast] Yoast seo not showing on some pages"

A screenshot would be very useful as it is not completely clear what you mean.
To make one, you can use the PrtScr button which on most keyboards is on the right top of the keyboard (next to scroll lock).
Alternatively if you use Firefox as your webbrowser, you can use for instance the excellent Screengrab addon. Similar utilities are available for most other browsers.