Meaning:
“打” here is used as a general verb meaning to “do” something in the similar case when we say “打车” (call a taxi), and “卡” means “card.” In most companies, employees are required to “打卡” (clock in and clock out) to record their working hours as an evaluation of their performance. Chinese netizens, however, have come up with a new meaning for the phrase. They use it to mean “completing a scheduled task in order to form a good habit or reach a goal,” most often in scenarios such as jogging to lose weight.
Example:
A: 你好象苗条了很多。
Nǐ hǎoxiàng miáotiáo le hěnduō。
You look much slimmer now.
B: 我已经坚持晨跑打卡两个月了，瘦了十公斤呢。
Wǒ yǐjīng jiānchí chénpǎo dǎkǎ liǎnggèyuè le，shòu le shí gōngjīn ne。
I’ve been sticking to my daily morning jogging routine for two months and already shed 10 kilograms.