My question is: What is the law for placing a topi, romal (scarf), tasbeeh, or any such things in a spot in the masjid to occupy that spot for oneself? If there is any verdict about this then please let me know.
The masjid is the house of Allahتعالی. All worshipers are equally deserving to perform their worship in any part of the masjid. Placing a topi, or chair etc. or perform worship in a specific spot in the masjid for some time doesn’t make one’s more deserving of that spot than other worshipers. For this reason, if someone comes and sits in any spot in the masjid, it is not proper for someone else coming afterwards to remove him from that spot. This must be avoided. However, if someone sits in a certain spot in the masjid and he has to get up from that spot due to some immediate necessity (e.g. Spitting, cleaning his nose, making wuzu etc.), and he places a cloth, tasbeeh or topi etc. on that spot before leaving, then it is not becoming for someone else to remove it and sit in that spot.
But if someone performs wuzu and doesn’t intend to remain in the masjid, instead he places something on that spot to secure it and then he leaves, then this is also not proper, and if someone else wants to remove what he placed in that spot and sit there, then he can do so. Afterwards, it will not be proper for the first person to remove him from that spot.
And Allah knows best.