How to List the Set of In-links to a Node

Simple pattern matching:

Cases[edges, edge : (v_ -> 5) :> v]

{27, 23, 22, 21, 4, 25, 7, 24, 30, 15, 18, 19, 29, 3, 8, 9, 10}

If you had specified the graph using DirectedEdge instead, then the pattern would have looked like this:

Cases[DirectedEdge @@@ edges, edge : DirectedEdge[v_, 5] :> v]

{27, 23, 22, 21, 4, 25, 7, 24, 30, 15, 18, 19, 29, 3, 8, 9, 10}

If you have a big graph, IncidenceList can be used to efficiently narrow it down to all edges that are incident to a given node:

Cases[
 IncidenceList[Graph[edges], 5],
 DirectedEdge[v_, 5] :> v
 ]

{27, 23, 22, 21, 4, 25, 7, 24, 30, 15, 18, 19, 29, 3, 8, 9, 10}

This leverages the graph functions even more:

g = Graph[edges];
m = IncidenceMatrix[g];
First /@ Extract[
  EdgeList[g],
  Position[m[[VertexIndex[g, 5], ;;]] // Normal, 1]
  ]

{27, 23, 22, 21, 4, 25, 7, 24, 30, 15, 18, 19, 29, 3, 8, 9, 10}

A few additional alternatives:

Rest @ VertexInComponent[edges, 5,1]

{27, 23, 22, 21, 4, 25, 7, 24, 30, 15, 18, 19, 29, 3, 8, 9, 10}

GroupBy[edges, Last -> First] @ 5

{27, 23, 22, 21, 4, 25, 7, 24, 30, 15, 18, 19, 29, 3, 8, 9, 10}

Rest @ DeleteDuplicates[5 /. List /@ Reverse /@ edges]

{27, 23, 22, 21, 4, 25, 7, 24, 30, 15, 18, 19, 29, 3, 8, 9, 10}

SparseArray[Reverse /@ List @@@ edges -> 1]["AdjacencyLists"][[5]]

{27, 23, 22, 21, 4, 25, 7, 24, 30, 15, 18, 19, 29, 3, 8, 9, 10}

Transpose[SparseArray[List @@@ edges -> 1]]["AdjacencyLists"][[5]]

{3, 4, 7, 8, 9, 10, 15, 18, 19, 21, 22, 23, 24, 25, 27, 29, 30}

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