If you want to get 20/20 full mark , then it will be Taairatun Khaassatun طائرةٌ خاصَّةٌ if you want to speak the daily speech , it's okay to say Taairah Khaassah ..

The first pronunciation is the correct and the standard one. The second is also correct and it is called the simplified Arabic; which is advised by Arabic didactic specialists. The advantages of this pronunciation is making speaking Arabic easy for both native and non-native speakers; because they don't have to apply all the grammar rules while speaking. So as a learner it is recommended for you to choose the second pronunciation if not sure of your grammar knowledge ,but when you become intermediate or advanced learner you have to apply as possible as you can grammar rules in words ending to make what you say or write more comprehensible and clear; because sometimes the meaning can be ambiguous: ضرب التلميذ المعلم dharaba atilmith almo'alim= ambiguous ضرب التلميذً المعلمُ dharaba atilmitha almo'alimu= clear dharaba = V atilmitha = Object almo'alimu = Subject بالتوفيق

number 1 is the correct one but when you speak in "fossha" which mean the correct accent with rules and grammers and every thing. and the number 2 is also correct when u speak without rules like native speaker they speak in there own accent. So when see the dhamma tanween (ٌ ) you pronounced it in the middle of sentence like number 1 and you do not pronounced it in the end of sentence and this the rule.