I am creating a lvl 2 wizard and I am questioning how many spells i can have in my spellbook (known spells not the prepared ones).

Information about Wizard spells can be found on its class page.

Spellbook

At 1st level, you have a spellbook containing six 1st-level wizard spells of your choice.

Learning Spells of 1st Level and Higher

Each time you gain a wizard level, you can add two wizard spells of your choice to your spellbook for free.

So at second level, you will have 8 wizard spells of your choice in your spellbook.

Unless you find a spell book then you can copy any new spells you find in that book into your own spell book.

Potentially you could also have spell scrolls as well to have more but temporary spells.

thx

The minimum number of spells you get for free is twice your wizard level + 4.

2nd level wizard: 2 x 2 = 4, +4 = 8.

6th level wizard: 6 x 2 = 12, +4 = 16.

You can also get spells through scribing them from scrolls, other wizard books, etc. 

Copying a Spell into the Book. When you find a wizard spell of 1st level or higher, you can add it to your spellbook if it is of a spell level you can prepare and if you can spare the time to decipher and copy it.

Copying that spell into your spellbook involves reproducing the basic form of the spell, then deciphering the unique system of notation used by the wizard who wrote it. You must practice the spell until you understand the sounds or gestures required, then transcribe it into your spellbook using your own notation.

For each level of the spell, the process takes 2 hours and costs 50 gp. The cost represents material components you expend as you experiment with the spell to master it, as well as the fine inks you need to record it. Once you have spent this time and money, you can prepare the spell just like your other spells.

From the PHB: Page 114.

Remember that as a 2nd-level Wizard, the spells you choose cannot be higher than 1st level.

So, as others have said, you start with 6, and you gain 2 every time you level up. The levels of the chosen spells can always be up to half of your level, rounded up. So at 3rd level, the chosen spells can be of either 1st or 2nd level, at 5th level, they can be 1st, 2nd, or 3rd level, etc. Spells can never be higher than 9th level.

Keep in mind that you have to prepare your spells before casting. At the end of a long rest, you can prepare a number of spells from your spellbook equal to your Wizard level + your Intelligence modifier.

As a wizard you can ritually cast any spell with the ritual tag in your spell book without having it prepared. At 2nd level you're likely to be able to prepare 5 or 6 spells but have 8 in your spell book. So if you add a few ritual spells to your spell book, such as detect magic or comprehend languages you'll have access to even more spells during the adventuring day than you can prepare.