We introduce the concept of Quantum Ping (QPing) as a diagnostic primitive for future quantum networks, designed to assess whether two or more end nodes can establish practical quantum entanglement under given resource and time constraints, with controlled overhead and time-adaptive fidelity thresholds. Unlike classical ping, which probes network-layer connectivity through ICMP messages, our proposed quantum version is adapted to the unique features of quantum networks, where connectivity depends on the availability and quality of shared entanglement. We develop a formal framework for QPing and leverage tools such as sequential hypothesis testing to probe quantum connectivity. We present several strategies, including active strategies with path-based and segment-based variants, and resource-based strategies that utilize pre-shared entangled resources. We further provide a quantitative performance evaluation of these strategies, including diagnostic cost, latency, and feasibility under time-dependent decoherence. QPing can serve as a flexible diagnostic building block for quantum networks, designed to operate alongside fundamental network operations and to accommodate different architectural assumptions and protocol design approaches.