Tesadüfen eski arkadaşımı parkta gördüm.

By chance, I saw my old friend in the park.

Breakdown of Tesadüfen eski arkadaşımı parkta gördüm.

• benim: my
• arkadaş: the friend
• park: the park
• eski: old

Questions & Answers about Tesadüfen eski arkadaşımı parkta gördüm.

What exactly does the word arkadaşımı consist of?

It’s built from three parts:

• arkadaş = friend
• -ım = my (1st person singular possessive)
• -ı = the accusative case (marks a specific/definite direct object)

So arkadaşımı means “my friend” as a definite object. Other useful forms:

• arkadaşım = my friend (no case)
• arkadaşıma = to my friend (dative)
• arkadaşımdan = from my friend (ablative)
• arkadaşımla = with my friend (comitative -la/-le)

Is the mı in arkadaşımı the yes/no question particle?

No. The -mı you see is not the question particle; it’s part of the possessive + accusative ending (-ım + -ı → -ımı).
The yes/no question particle (mı/mi/mu/mü) is a separate word and is written separately:

• Onu gördün mü? = Did you see him/her?
• Arkadaşımı mı gördün? = Was it my friend that you saw? (Here mı is separate.)

Why is the object marked with the accusative (-ı)?