I used this code a while back to find DynamicContent that has been related to another DynamicContent by Guid[]

RelatedDynamicContent.cs

//This feature is available out of the box in Sitefinity 7+

public DynamicContent CurrentFeature;

protected override void InitializeControls(GenericContainer container)
{
    CurrentFeature = this.ResolveDetailItemFromUrl();

    if (CurrentFeature != null)
    {
        var relatedCapabilities = RetrieveRelatedCapabilities(CurrentFeature);

        if (relatedCapabilities.Count() > 0)
        {
            CapabilityRepeater.Visible = true;
            CapabilityRepeater.DataSource = relatedCapabilities;
        }
    }
}

protected virtual DynamicContent ResolveDetailItemFromUrl()
{
    var itemUrl = this.GetUrlParameterString(true);
    if (itemUrl != null)
    {
        var urlName = itemUrl.Substring(itemUrl.LastIndexOf('/') + 1);

        var providerName = String.Empty;
        DynamicModuleManager dynamicModuleManager = DynamicModuleManager.GetManager(providerName);
        Type featureType = TypeResolutionService.ResolveType("Telerik.Sitefinity.DynamicTypes.Model.Features.Feature");

        var feature = dynamicModuleManager.GetDataItems(featureType).Where(f => f.UrlName == urlName).FirstOrDefault(); 
        
        if (feature != null)
        {
            return feature;
        }
    }

    return null;
}

private IQueryable<DynamicContent> RetrieveRelatedCapabilities(DynamicContent feature)
{
    var providerName = String.Empty;
    DynamicModuleManager dynamicModuleManager = DynamicModuleManager.GetManager(providerName);
    Type capabilityType = TypeResolutionService.ResolveType("Telerik.Sitefinity.DynamicTypes.Model.Capabilities.Capability");

    var myCollection = dynamicModuleManager.GetDataItems(capabilityType).Where(c => c.GetValue<Guid[]>("Features").Contains(feature.Id) && c.Status == ContentLifecycleStatus.Live);

    return myCollection;
}