You need to count the number of arcade game and trivia badges (circular ones) you've earned, each badge will earn you 1 point. Also, skill badges (not completion badges, except it is a special event like now) will fetch you points, complete 2 of them and you'll get one point. Special arcade game badges which look a bit different from the regular badges can fetch you 2 points.
You can always verify which arcade badge contains how many points as the number of points per badge is mentioned there in the arcade page by default.
Also, there are many events where you can earn extra points by completing challenges, like the facilitator program. And do look out for the Arcade Insider mails (you'll get it only if you've subscribed to Arcade) where they'll mention the number of points you've collected. They might even give you free credits to complete labs there!
Even then if you feel like you are unable to calculate, there are the shortcut ways: there are third-party points calculator available in the internet, though they might not give accurate info. Rather, just post your Qwiklabs public profile link here and anyone of us can help you out!
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