I have the blockchain in one wallet, but it's not most recent.
I had written "addnode=IP" to config file (where IP - is IP of my computer with wallet which have the blockchain), but another wallet didn't see it.
If I'll use "addnode=IP:PORT" command, what PORT number I should to write?
You can't sync 2 clients if none of them is a node (a client with most recent block chain).
To sync, you need at least one node that has most recent block chain and the node has to be online when you try to sync.
(Try comparing this to how torrents work. If 2 peers are exchanging data through P2P protocol, but none of them have 1 complete copy of the data, none of them will ever complete the download to 100%)
The best you can do is go to the official site (or their official thread here) and request IP of an active node. If there isn't one, you're out of luck.