Cronjob run every two weeks, on Saturday, starting on this saturday

0 8 * * 6 test $((10#$(date +\%W)\%2)) -eq 1 && yourCommand

date +%W: week number of year with Monday as first day of week, today week 39

10#$(date +%W): conver the date +W to decimal number and avoid shell base parsing confusion

$((39%2)): modulo operation: result is 0 (even week number) or 1 (odd week number), this week result is 1, next week 0

test 1 -eq 1: arithmetic test (equal), in this case result is boolean true

&& yourCommand: Boolean AND: run yourCommand only if result of previous command was boolean true

Note that the year can get two odd weeks: 53 (this year) and 1 (next year)

What you've shown is "every week". Then the code is:

0 8 * * 6

Are you sure you need to run it every two weeks?

0 8 * * 6 expr `date +\%s` / 604800 \% 2 >/dev/null || yourCommand