The quickest way is to hit either:
''
(two apostrophes) or:
``
(two backticks). Note that the difference is that the backtick goes to the same location on the line, whereas the apostrophe goes to the start of the line. On a UK keyboard, the apostrophe is more accessible, so I tend to use that one. There are loads of useful marks like this, see :help mark-motions.
For some other motions (not 2j I think), there’s also the jump-list that lets you navigate back and forth among a number of motions. CtrlO and CtrlI do this navigation, but see :help jump-motions for more information.