Hi Ralf,
At the moment we haven't implemented click/select events for PivotMatrix yet. In the meantime you could check our map property to get all information for each aggregated cell:
https://www.koolreport.com/docs/pivot/pivottable_and_pivotmatrix/#properties-map-(version-%3E=-5.0.0)
An example value for a $cellInfor is:
{
    "row": {
        "customerName": {
            "childOrder": "3",
            "value": "Auto Canal+ Petit",
            "numChildren": 1,
            "numLeaf": 1
        },
        "productLine": {
            "value": "{{all}}",
            "total": true,
            "numChildren": 1,
            "numLeaf": 1,
            "level": 2,
            "childOrder": 1
        },
        "productName": {
            "value": "{{all}}",
            "total": true
        },
        "hasTotal": true,
        "fieldOrder": 0
    },
    "column": {
        "orderYear": {
            "numChildren": 2,
            "numLeaf": 2,
            "childOrder": "1",
            "value": 2004
        },
        "orderMonth": {
            "childOrder": "1.1",
            "value": "{{all}}",
            "total": true,
            "numChildren": 2,
            "numLeaf": 2,
            "level": 1
        },
        "hasTotal": true,
        "fieldOrder": 0
    },
}
Let us know if it could help your case. Thanks!