Display the location of an item in a project.

This snippet gets the fontFamily of selected text layer. Then loops through all the compositions in the project and collects all layers that matche fontFamily.

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(function() {
    // Get active composition
    var composition = app.project.activeItem;
    if (!composition || !isComposition(composition))
        return alert("Please select composition first");
    // Get selected layer and make sure it's a Text Layer
    var layer = composition.selectedLayers[0];
    if (!layer || !isTextLayer(layer)) {
        return alert("Please select a text layer.");
    }
    // Get font family
    var fontFamily = getFontFamily(layer);
    var layersThatMatchFontFamily = [];
    // Loop through all the comps and collect all text layers
    // witch matches fontFamily;
    var allCompositions = getAllCompositions();
    for (var i = 0, il = allCompositions.length; i < il; i++) {
        composition = allCompositions;
        for (var j = 1, jl = composition.numLayers; j <= jl; j++) {
            layer = composition.layer(j);
            if (isTextLayer(layer) && getFontFamily(layer) === fontFamily) {
                layersThatMatchFontFamily.push(layer);
            }
        }
    }
    // Done.
    var message = "Font \"" + fontFamily + "\" has been used " + layersThatMatchFontFamily.length + " times.\n";
    message += buildLocation(layersThatMatchFontFamily).join("\n");
    alert(message);
    function isTextLayer(layer) {
        return layer instanceof TextLayer;
    }
    function isComposition(item) {
        return item instanceof CompItem;
    }
    function getFontFamily(textLayer) {
        var textDocument, textValue, fontFamily;
        textDocument = textLayer.property("ADBE Text Properties").property("ADBE Text Document");
        textValue = textDocument.value;
        fontFamily = textValue.fontFamily;
        return fontFamily;
    }
    function getAllCompositions() {
        var composition, compositions;
        compositions = [];
        for (var i = 1, il = app.project.numItems; i <= il; i++) {
            composition = app.project.item(i);
            if (isComposition(composition)) {
                compositions.push(composition);
            }
        }
        return compositions;
    }
    function buildLocation(layers) {
        var layer, locations;
        locations = [];
        for (var i = 0, il = layers.length; i < il; i++) {
            layer = layers;
            locations.push(layer.containingComp.name + " > " + layer.name);
        }
        return locations;
    }
})();