The set of combinations is the collection of all subsets of $\{1,2,\ldots,n\}$ of size $k$; if we let $[n]=\{1,2,\ldots,n\}$ (more or less common, depending on the context) $\mathcal{P}(X)$ denote the set of all subsets of $X$, then you are looking for the set
$$\bigl\{ A\in\mathcal{P}([n])\bigm| |A|=k\bigr\}.$$
I do not think there is any particular notation for it, but
$$\mathcal{P}_k([n])$$
seems reasonable enough. You would have to specify it, though.
For permutations, the order matters. So you are looking for the set of all function $f\colon[k]\to[n]$ that are one-to-one. Again, there is no standard notation, but the set of all functions is $[n]^{[k]}$, so you would want
$$\bigl\{ f\in [n]^{[k]}\bigm| f\text{ is one-to-one}\bigr\}.$$
Equivalently, you would want all $k$-tuples that have $k$-distinct elements. So, using the previous notation for subsets of size $k$, you would have:
$$\bigl\{ f\in[n]^{[k]}\bigm| f([k]) \in \mathcal{P}_k([n])\bigr\}.$$