As a Christian the simple answer is that it is OK to visit a Sikh Temple for a wedding. However it is not the whole answer. This is an issue that Paul had to deal with in Corinth. Although it had to do with eating meat sacrificed to idols, the priciples are the same and worth understanding.
In 1 Corinthians 8, Pauls says that things like eating meat sacrificed to idols (or in our case visiting the temple of another ‘god’), should not worry a Christian because Jesus is ‘bigger’ than these things and has overcome them. So as a Christian we are free to eat or visit.
However not all Christians may see it like this or understand the freedom we have Christ. Such people may be offended by our actions or even tempted to go against their consciences and sin. We must ensure that our actions do not lead to such an outcome. So Paul concludes in 1 Corinthians 8:9: “Be careful, however, that the exercise of you freedom does not bcome a stumbling block to the weak”.
So while you are free to visit the Sikh temple for a wedding, I woulld be careful to make sure your Christian friends and church members are not offended by it.
I hope this is helpful.