why can players use certain skins. like I see xpecial stream and he can use a 
skin but when I see him in the lcs he never has it on? is there anything to it or is it against the rules?
what is the next victorious skin last time it was 
. I am working my way up and I need to get the champion that the new skin is for.
The lcs players can only use skins enabled for them in their client. Riot has disabled certain skins for various reasons but one of the big ones is that certain skins make it harder to distinguish certain champs and their skills. However for , I know his championship skin is disabled for a soul color/texture bug. Hope this helps, just the bits and pieces I've gather from lcs players talking about the subject.
Concerning the Victorious skin: if you don't own the champion, but you're rewarded the skin for getting into Gold tier, you're automatically given the champion. For example, if you were in Gold at the end of S3 but didn't own Elise, you'd have gotten Elise and the skin for free.
LCS players can only use skins available in the store. For example, they have been using the world cup skins lately in LCS, but after the skins become unavailable, they wont be allowed to use them anymore. I guess it is part of their marketing. Skins that cause issues when it comes to visuals are also not allowed, such as steel legion 
.
Regarding your need to purchase the next champion that the victorious skin is for, you dont need to worry about that. If you qualify for a victorious skin and you dont own that champion, you will receive both at no additional cost.
Riot has stated before that certain skins are banned from LCS play, usually because their particle effects are hard to see (ie Snow Day Ziggs). There's a full list of which skins are banned somewhere.
Yes, some skins are not allowed in the LCS. This can be the case to compensate for bugs or animations not lining up or drastic color changes. For example, Arcade Sona is the only Sona skin allowed in OGN because the other skins' ult animations do not line up with the hitbox correctly. Also, PF Ezreal is not allowed in the LCS because the drastic changes to his model.
And if you achieve Gold before the season ends, you will receive both the Victorious skin AND that champion if you don't already own them.
