How can we motivate the other 22 NATO member nations to meet their 2% GDP?

It's pretty sad that countries like Greece, given its recent issues, and Turkey have met their commitment every year since 1991, and a country like Estonia that has been getting on its feet since leaving the USSR meets it, even if it's inconsistently. But countries like The Netherlands, Denmark, Norway, and Luxembourg, which are 4 of the top 10 richest countries in Europe, either don't meet the commitment or barely contribute at all.

Probably some sort of reverse carrot before the horse concept. Pull back from cross training, exercises, financial support etc. with countries that aren't living up to obligations and shift emphasis to countries that are. In the short term this isn't going to impact NATO operations, but will send the message that unless obligations are met their country will become second or third class members of the organization. In the long term NATO will learn to operate with less emphasis on support to countries not living up to their obligations.

Three fold approach.
1:If we currently provide aid to one of those countries, all future payments will have the amount of Their last NATO alliance support deficit deducted post approved aid $$ amounts. IOW, if US Congress approves $1 mil in aid Marquezina in FY 19... and Marquezina had pledged $.8mil in NATO support FY 18, but transfered NONE, the US will provide no more than $.2 mil for FY 19 to Marquezina
2: Lean on other NATO countries to lobby the deficit ones... any country two years behind in NATO pledges will go on a list, said list and the $ amount deficit will be added up annually, and the US pledge overall to NATO will be reduced that amount for next FY.
3: De-fund NATO, evict them from the US HQ facilities. If they wish to purchase with hard cash the facility at fair market value, or other such property in the US , Fine. But no tax deals, no US appropriated funds will be used, no legal exceptions for NATO members in the US, they pay for license plate, pay parking tickets, their visiting members must have a valid visa, approved though the same system used by some potential immigrant in new Deli. No FREE LUNCH.