Tashahhud in a Two-Rak’ah Prayer: What to Say?
Question

In a two rak’ah prayer, what should the worshipper say in the Tashahhud? Should he say the first or the second, or both of them together, and with which one should he start?
Praise be to Allah.In a two-rak’ah prayer, the worshipper should say the Tashahhud , and this is one of the versions:
Al-Tahiyyatu Lillahi wa’l-salawatu wa’l-tayyibat. Al-salamu ‘alayka ayyuha’l-Nabiyyu wa rahmat-Allahi wa barakatuhu. Al-salamu 'alayna wa ‘ala ‘ibad-illah il-salihin. Ash-hadu an la ilaha ill-Allah wa ash-hadu anna Muhammadan ‘abduhu wa rasuluh (All compliments, prayers and pure words are due to Allah. Peace be upon you, O Prophet, and the mercy of Allah and His blessings. Peace be upon us and upon the righteous slaves of Allah. I bear witness that there is no god except Allah and I bear witness that Muhammad is His slave and Messenger). ((al-Bukhari, 831; Muslim, 402)  
Then after that he should send blessings upon the Prophet (blessings and peace of Allah be upon him) and say:  
“Allahumma salli ‘ala Muhammad wa ‘ala ali Muhammad kama salayta ‘ala Ibrahim wa ‘ala ali Ibrahim , innaka hamidun majid. Allahumma barik ‘ala Muhammad wa ‘ala ali Muhammad kama barakta ‘ala Ibrahim wa ‘ala ali Ibrahim, innaka hamidun majid (O Allah, send prayers upon Muhammad and upon the family of Muhammad, as You sent prayers upon Ibrahim and the family of Ibrahim, You are indeed Worthy of Praise, Full of Glory. O Allah, bless Muhammad and the family of Muhammad as You blessed Ibrahim and the family of Ibrahim, You are indeed Worthy of Praise, Full of Glory). (Al-Bukhari, 3370; Muslim, 406)  
Then he should recite the following du’a:
Allahumma inni a’udhu bika min ‘adhabi jahannam wa a’udhu bika min ‘adhab il-qabr, wa a’udhu bika min fitnat il-masih il-dajjal, wa a’udhu bika min fitnat il-mahya wa’l-mamat wa a’udhu bika min al-matham wa’l-maghram (O Allah, I seek refuge in You from the torment of Hell, and I seek refuge in You from the torment of the grave, and I seek refuge in You from the tribulation of the Dajjal, and I seek refuge in You from the trials of life and death, and I seek refuge in You from falling into sin and debt.) (Al-Bukhari, 833; Muslim, 588) 
Then after that he may make du’a as he likes , asking for good in this world and in the Hereafter. And if he recites some of the du’as narrated in the Sunnah, that is better. 
For more about tashahhud, please see these answers: 95798 , 125897 , and 11527 .
And Allah knows best.