So England has attacked Denmark with a fleet in the Skagaric support from Helgoland Bigbt and the North Sea. Russia has attacked the Skagaric from the Baltic Sea and with support from Sweden and the German fleet in Denmark. Would the offensive prevail?
The Baltic Sea is not adjacent to Skaggerak, so the Russian move is invalid. Around Denmark, England attacks with two uncut supports, so a total strength of 3. Denmark would need at least two defensive supports to stay, so the English attack prevails.
Even if the Russian unit moving to Skaggerak was moved to Norway to make it a valid move, this would not affect the situation in Denmark.
In general you can check the outcome of any situation you desire at Stabbeurfou (this is not the only sandbox out there online that you can use, I believe at least Backstabbr has one too)
The Diplomacy rulebook (pdf) is also available online to help you.