what does aman aman mean? or just aman 

?

Here is my understanding, hopefully someone with stronger Turkish will also respond.

I believe it is similar to "my goodness!".

Aman aman would be similar to just adding more empasis or how Turkish people often repeat in conversation. Just as you may hear "evet, evet" or "yok, yok".

Hello! I´m a native Turkish-speaker and I think I can answer that question. ^^

"Aman!" means more like "Yikes!" or "Ouch!", we use it in case of danger. For ex: if you see someone tripping over some stairs, you exclaim: "Aman! Dikkat et!" (Careful!)

But "aman aman" has a totally different meaning. In familiar language ("sokak ağzı" or "halk dili") it means "significant" or "fancy". It´s mostly used in this form: "Öyle aman aman bir şey değil!" which means "it´s nothing fancy." Here´s a further example to understand better:

"Öyle aman aman bir şey almana gerek yok, işini görsün yeter." -- You don´t need to buy anything fancy, just something decent/just something that´ll suit your needs would suffice.

Hope it was helpful,

-Jansay

Thank you so much