From the notation of your question I assume you are using Mathematica and not WolframAlpha to do this.

If so then look up ReplaceAll in the Mathematica documentation.

ReplaceAll[2 Cos[v] + 2 Cos[v]*Log[u Sin[v]], {u->8, v->5}]

Many functions in Mathematica have an abbreviated form, like this one for ReplaceAll.

2 Cos[v] + 2 Cos[v]*Log[u Sin[v]]/.{u->8, v->5}

Using the abbreviated form can be somewhat confusing for a new user and sometimes the documentation doesn't clearly show the use of both the un-abbreviated and the abbreviated forms, but if you can understand one way of getting what you need then make some notes for future reference and do whatever works for you.

If you want that result converted into decimals then look up the N function in the documentation.

Then you may or may not want to think about why the result is a complex number.