Here is the syrup I use when I am assembling layered cakes or prepping a cake surface for frosting.
1 cup water
1/4 cup sugar
1 tbsp lemon juice
In a saucepan mix all the ingredients and bring to boil on medium high. Keep stirring to make sure the sugar dissolves well. Once it starts boiling, let it continue for a minute or two. Switch off heat and you are ready with your syrup
If for some reason you do not want to use this syrup, feel free to mix up 2 tbsp of any jam (not marmalade or preserves) with 5-6 tbsp of water and prepare a syrup to use for assembling a cake.