I am a Pakistani national and holder of a multiple entry US/Schengen visa, can I travel to northern Cyprus (Lefkosa via Ercan International airport) on a Turkish e-visa?
You don't need a Turkish e-visa, just a valid Pakistani passport.
No one except Armenians and Nigerians need a visa to visit North Cyprus.
However, be warned that, when checking in for the flight to Turkey (because you need to connect there), because North Cyprus isn't recognised by the international community, when Ercan is selected as the destination in the database, the rules for South Cyprus will appear. Therefore, it will first look like you need a visa.
HOWEVER, further down it says:
Warning: - These entry regulations apply only to the part of Cyprus controlled by the government of Cyprus (i.e. they are not applicable at Ercan (ECN) and at Gercitkale (GEC)). - For entry regulations applicable at Ercan (ECN), see: http://mfa.gov.ct.tr/consular-info/visa-regulations/
And in that link, it says (admittedly not in clear, direct terms) that only Armenians and Nigerians need a visa.
As for transiting Turkey:
TWOV (Transit Without Visa): - Passengers with a confirmed onward ticket for a flight to a third country within 24 hours. They must stay in the international transit area of the airport and have documents required for the next destination.
So again, you only need your passport, but be prepared to have to point to the TIMATIC sections I quoted (the check-in staff will see it)
Thanks a lot for your help. I have checked with Turkish e-visa section and this is what they said which quite complies with what you guys suggested.
"If you will go to Turkish Republic of Northern Cyprus through Turkey, you may use an e-Visa to travel. However, if you will go directly to Turkish Republic of Northern Cyprus, kindly proceed to the nearest Turkish mission to complete a visa application"
So just to be on safe side, i will take a Turkish e-visa and fly via Istanbul to TRNC.