log-likelihhood function for N sample of data
I’m assuming that the trace is what is confusing, so let me give you some clues.

First an identity $$ Trace(\mathbf{ABC)})= Trace(\mathbf{BCA}) $$  

and for scaler $x$, 
$$ Trace(x) =x$$

Let $\mathbf{a}$ and $\mathbf{b}$ be $N \times 1$ vectors and $\mathbf{C} $is a $N \times N$ matrix, so $$ \mathbf{ a^T C b} = Trace ( \mathbf 
{C \,b a^T}) $$

The rest you should be able to figure out using the definition of a Gaussian, independence, and properties of the log.