You got to visit/call our embassy there. Talk with the defence attachee.
Being abroad, you are exempted from initial testing and will be reuired to go through ISSB only. But you got to give them an address in Pakistan coz they wont send you call up letters abroad.
As for the citizenship, yes you would be required to renonce it, BUT only after you have been recommended by the ISSB, joined PMA and completed your training successfully. i.e just a few weeks before you are to pass out from the academy/get commissioned.
This is to ensure that you dont lose your citizenship for nothing if you are withdrawn from the academy on any grounds(medical, discipline etc).
vist joinpakistanarmy.gov.pk for more details.
For exact dates, you need to keep an eye on the website, as it is not possible to pin point them.
Feel free to ask any further querries.
Lastly, if you are already double minded so as to join the army or become the next desi punjabi singer, as advised by a few members, then i must warn you that you have already failed your ISSB. So, be sure of what you want to do before you funally decide. Half hearted atempts will get you nothing from the army.