My question is how to pronounce kanataa ithnatayn correctly, and how we can show by reading, that it is dual feminine..

Assalamu Alaikum

My question is how to pronounce correctly, And how we can show by reading, that it is dual feminine gender, when hamza wasl is coming after it. 

Jazakallah khairan. 

Answer

Wa alaikum assalaam wa rahmatullahi wa barakatuh,

To pronounce these two words we pronounce the  on the  and then immediately go to the  saakinah of the word because the hamzah al-wasl is not pronounced when continuing reading.  The alif represented the dual form of the verb is dropped in pronunciation because of the rule when two saakin letters meet between two words.  The voweling shows that it a dual female verb because there is a  on the.  If it were singular, the word would have acquired a kasrah on the normally saakin  because of the Arabic rule of forbiddance of two saakin letters between two words.   Therefore the singular female and dual would have different vowels on the so nothing is needed to show that it is dual female gender.  .   

To read more about the rules for two saakin letters meeting between two words see the following q&a: http://www.abouttajweed.com/121003.htm

Wa iyyaakum

Wa assalaam alaikum.