1)To what type i must convert nonce 00000000 to get 2e6b0a1d???
Not sure what you are asking here. A miner will start at nonce 0 and try all 2^32 possibilities until it reaches 4294967295. This allows multiple hashes per blockheader change. Once all nonces have been tried
2) In some examples i have seen target: ffffffffffffffffffffffffffffffffffffffffffffffffffffffff00000000 How i know is my solution smaller than target?
You reverse it again and compare the values (they are hexadecimal)
These would be smaller
00000000.... anything else here is less.....
These would be too large
00000001 .... anything else here is too large ...
Since only the most significant digits matter generally you can break the hash into 32 bit "cunks" and just compare them.
so to match your example target the first 32bit must be 00000000. Anything other than 0 is too large.
Since second 32bit segment is ffffffff then any value is good (no need to check 2nd to 8th segments).
On the other hand if you target was
which reverses to
then you would need to check that first segment is <= 00000000
and second segment <= afffffff